Persistent data structures

ABSTRACT

Apparatuses, systems, methods, and computer program products are disclosed for a persistent data structure. A method includes associating a logical identifier with a data structure. A method includes writing data of a data structure to a first region of a volatile memory module. A volatile memory module may be configured to ensure that data is preserved in response to a trigger. A method includes copying data of a data structure from a volatile memory module to a non-volatile storage medium such that the data of the data structure remains associated with a logical identifier.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/864,514 entitled “PERSISTENT DATA STRUCTURES” andfiled on Aug. 9, 2013 for Nisha Talagala, et al., of U.S. ProvisionalPatent Application No. 61/878,031 entitled “PERSISTENT MEMORYMANAGEMENT” and filed on Sep. 15, 2013 for Nisha Talagala, et al., is acontinuation-in-part of U.S. patent application Ser. No. 13/836,826 (nowU.S. Pat. No. 9,208,071) entitled “APPARATUS, SYSTEM, AND METHOD FORACCESSING AUTO-COMMIT MEMORY” and filed on Mar. 15, 2013 for NishaTalagala, et al., is a continuation-in-part of U.S. patent applicationSer. No. 13/838,070 (now U.S. Pat. No. 9,218,278) entitled “APPARATUS,SYSTEM, AND METHOD FOR AUTO-COMMIT MEMORY MANAGEMENT” and filed on Mar.15, 2013 for Nisha Talagala, et al., and is a continuation-in-part ofU.S. patent application Ser. No. 13/694,000 (now U.S. Pat. No.9,047,178) entitled “APPARATUS, SYSTEM, AND METHOD FOR AUTO-COMMITMEMORY MANAGEMENT” and filed on Dec. 4, 2012 for Nisha Talagala, et al.,which claims the benefit of U.S. Provisional Patent Application No.61/583,133 entitled “APPARATUS, SYSTEM, AND METHOD FOR AUTO-COMMITMEMORY” and filed on Jan. 4, 2012 for David Flynn, et al., of U.S.Provisional Patent Application No. 61/637,257 entitled “APPARATUS,SYSTEM, AND METHOD FOR AUTO-COMMIT MEMORY” and filed on Apr. 23, 2012for David Flynn, et al., of U.S. Provisional Patent Application No.61/661,742 entitled “APPARATUS, SYSTEM, AND METHOD FOR AUTO-COMMITMEMORY” and filed on Jun. 19, 2012 for Nisha Talagala, et al., of U.S.Provisional Patent Application No. 61/691,221 entitled “APPARATUS,SYSTEM, AND METHOD FOR AUTO-COMMIT MEMORY” and filed on Aug. 20, 2012for Nisha Talagala, et al., of U.S. Provisional Patent Application No.61/705,058 entitled “APPARATUS, SYSTEM, AND METHOD FOR SNAPSHOTS IN ASTORAGE DEVICE” and filed on Sep. 24, 2012 for Nisha Talagala, et al.,and is a continuation-in-part of U.S. patent application Ser. No.13/324,942 (now U.S. Pat. No. 8,527,693) entitled “APPARATUS, SYSTEM,AND METHOD FOR AUTO-COMMIT MEMORY” and filed on Dec. 13, 2011 for DavidFlynn, et al., which claims the benefit of U.S. Provisional PatentApplication No. 61/422,635 entitled “APPARATUS, SYSTEM, AND METHOD FORAUTO-COMMIT MEMORY” and filed on Dec. 13, 2010 for David Flynn, et al.,each of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to data structures and more particularly topersistently storing data structures.

BACKGROUND

Data structures are often used by applications to organize and trackdata as the applications execute. The data structures are usuallyvolatile and are simply re-declared each time an application runs.Because of their traditionally volatile nature, little care is taken toensure that data structures are protected and not inadvertentlyoverwritten.

For example, an erroneous write using the wrong pointer may overwrite adata structure or portion of a data structure in volatile memory.However, because the data structure is volatile anyway, an applicationmay do little or nothing to protect integrity of the data structure.

Additionally, applications may benefit from the data of a data structureduring a subsequent execution. If a volatile data structure is lost,especially due to a power failure or improper shutdown, the executionstate or other data of an application may also be lost.

SUMMARY

Methods for a persistent data structure are presented. In oneembodiment, a method includes associating a logical identifier with adata structure. A method, in a further embodiment, includes writing dataof a data structure to a first region of a volatile memory module. Avolatile memory module, in certain embodiments, is configured to ensurethat data is preserved in response to a trigger. A method, in anotherembodiment, includes copying data of a data structure from a volatilememory module to a non-volatile storage medium so that the data of thedata structure remains associated with a logical identifier.

Another method for a persistent data structure is presented. In oneembodiment, a method includes associating a logical identifier with adata structure. A method, in a further embodiment, includes storing adata structure in a volatile memory device configured to ensure that thedata structure is preserved in response to a change in state. In certainembodiments, a method includes copying a data structure from a volatilememory device to a non-volatile storage medium so that the datastructure remains associated with a logical identifier.

Apparatuses for a persistent data structure are presented. In oneembodiment, an allocation module is configured to initialize apersistent transaction log in response to a request. A write module, incertain embodiments, is configured to append data to a persistenttransaction log by writing the appended data to a volatile memoryconfigured to ensure persistence of the data. In a further embodiment,an enforcement module is configured to enforce one or more rulespreventing data from being overwritten in a persistent transaction log.

Another apparatus for a persistent data structure is presented. Anapparatus, in one embodiment, includes means for satisfying one or morerequests for a persistent data structure. A persistent data structure,in certain embodiments, comprises data stored in a volatile buffer anddata stored in a non-volatile recording medium. In a further embodiment,an apparatus includes means for committing data stored in a volatilebuffer to a non-volatile recording medium. An apparatus, in anotherembodiment, includes means for providing access to a persistent datastructure from a non-volatile recording medium after a restart eventusing a logical identifier associated with the persistent datastructure.

A further apparatus for a persistent data structure is presented. In oneembodiment, an auto-commit memory module is configured to commit datafrom one or more memory buffers to a non-volatile storage device inresponse to a commit event. A persistent data structure module, incertain embodiments, is configured to provide data for a persistent datastructure to an auto-commit memory module for writing to one or morememory buffers so that the persistent data structure is committed to anon-volatile storage device.

Computer program products comprising a computer readable storage mediumstoring computer usable program code executable to perform operationsfor a persistent data structure is also presented. In one embodiment, anoperation includes providing access to a persistent log using a logicalidentifier. An operation, in a further embodiment, includes bufferingdata appended to a persistent log in a volatile memory. A volatilememory, in certain embodiments, may be configured to auto-commitbuffered data to a non-volatile storage medium in response to a committrigger. In another embodiment, an operation includes copying thebuffered data from the volatile memory to the non-volatile storagemedium such that the data of the persistent log remains associated withthe logical identifier.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of this disclosure will be readilyunderstood, a more particular description of the disclosure brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the disclosure and are nottherefore to be considered to be limiting of its scope, the disclosurewill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem for persistent data structures;

FIG. 2 is a block diagram illustrating another embodiment of a systemfor persistent data structures;

FIG. 3 is a block diagram of a further embodiment of a system forpersistent data structures;

FIG. 4 is a block diagram of a system comprising a plurality ofauto-commit memories;

FIG. 5 is a block diagram of an auto-commit memory implemented with acommit management apparatus;

FIG. 6 is a block diagram of another embodiment of a system forpersistent data structures;

FIG. 7 is a flow diagram of one embodiment of a method for auto-commitmemory;

FIG. 8 is a flow diagram of another embodiment of a method forauto-commit memory;

FIG. 9 is a flow diagram of another embodiment of a method forauto-commit memory;

FIG. 10A is a schematic block diagram illustrating one embodiment of apersistent data structure module;

FIG. 10B is a schematic block diagram illustrating another embodiment ofa persistent data structure module;

FIG. 11 is a schematic block diagram illustrating one embodiment of amapping structure, a sparse logical address space, and a log-basedwriting structure;

FIG. 12 is a schematic flow chart diagram illustrating one embodiment ofa method for a persistent data structure; and

FIG. 13 is a schematic flow chart diagram illustrating anotherembodiment of a method for a persistent data structure.

DETAILED DESCRIPTION

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present disclosure should be or are in anysingle embodiment of the disclosure. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present disclosure. Thus,discussion of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe disclosure may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize that thedisclosure may be practiced without one or more of the specific featuresor advantages of a particular embodiment. In other instances, additionalfeatures and advantages may be recognized in certain embodiments thatmay not be present in all embodiments of the disclosure. These featuresand advantages of the present invention will become more fully apparentfrom the following description and appended claims, or may be learned bythe practice of the disclosure as set forth hereinafter.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.Where a module or portions of a module are implemented in software, thesoftware portions are stored on one or more computer readable media.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

Reference to a computer readable medium may take any form capable ofstoring machine-readable instructions on a digital processing apparatus.A computer readable medium may be embodied by a compact disk,digital-video disk, a magnetic tape, a Bernoulli drive, a magnetic disk,a punch card, flash memory, integrated circuits, or other digitalprocessing apparatus memory device.

Furthermore, the described features, structures, or characteristics ofthe disclosure may be combined in any suitable manner in one or moreembodiments. In the following description, numerous specific details areprovided, such as examples of programming, software modules, userselections, network transactions, database queries, database structures,hardware modules, hardware circuits, hardware chips, etc., to provide athorough understanding of embodiments of the disclosure. One skilled inthe relevant art will recognize, however, that the disclosure may bepracticed without one or more of the specific details, or with othermethods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the disclosure.

The schematic flow chart diagrams included herein are generally setforth as logical flow chart diagrams. As such, the depicted order andlabeled steps are indicative of one embodiment of the presented method.Other steps and methods may be conceived that are equivalent infunction, logic, or effect to one or more steps, or portions thereof, ofthe illustrated method. Additionally, the format and symbols employedare provided to explain the logical steps of the method and areunderstood not to limit the scope of the method. Although various arrowtypes and line types may be employed in the flow chart diagrams, theyare understood not to limit the scope of the corresponding method.Indeed, some arrows or other connectors may be used to indicate only thelogical flow of the method. For instance, an arrow may indicate awaiting or monitoring period of unspecified duration between enumeratedsteps of the depicted method. Additionally, the order in which aparticular method occurs may or may not strictly adhere to the order ofthe corresponding steps shown.

FIG. 1 depicts one embodiment of a system 100 for preserving a datastructure. In certain embodiments, the system 100 preserves data and/orprovides power management even in the event of a power failure, powerreduction, or other power loss. In the depicted embodiment, the system100 includes a host computing device 114 and a storage device 102. Thehost 114 may be a computer such as a server, laptop, desktop, or othercomputing device. The host 114 may include components such as memory,processors, buses, and other components.

The host 114 stores data in the storage device 102 and communicates datawith the storage device 102 via a communications connection (not shown).The storage device 102 may be internal to the host 114 or external tothe host 114. The communications connection may be a bus, a network, orother manner of connection allowing the transfer of data between thehost 114 and the storage device 102. In one embodiment, the storagedevice 102 is connected to the host 114 by a PCI connection such as PCIexpress (PCI-e). The storage device 102 may be a card that plugs into aPCI-e connection on the host 114.

The storage device 102 also has a primary power connection 130 thatconnects the storage device 102 with a primary power source thatprovides the storage device 102 with the power that it needs to performdata storage operations such as reads, writes, erases, or the like. Thestorage device 102, under normal operating conditions, receives thenecessary power from the primary power source over the primary powerconnection 130. In certain embodiments, such as the embodiment shown inFIG. 1, the primary power connection 130 connects the storage device 102to the host 114, and the host 114 acts as the primary power source thatsupplies the storage device 102 with power. In certain embodiments, theprimary power connection 130 and the communications connection discussedabove are part of the same physical connection between the host 114 andthe storage device 102. For example, the storage device 102 may receivepower over a PCI connection.

In other embodiments, the storage device 102 may connect to an externalpower supply via the primary power connection 130. For example, theprimary power connection 130 may connect the storage device 102 with aprimary power source that is a power converter (often called a powerbrick). Those in the art will appreciate that there are various ways bywhich a storage device 102 may receive power, and the variety of devicesthat can act as the primary power source for the storage device 102.

The storage device 102 provides non-volatile storage, memory, and/orrecording media 110 for the host 114. FIG. 1 depicts the storage device102 comprising a write data pipeline 106, a read data pipeline 108,non-volatile memory 110, a storage controller 104, a persistent datastructure module 1009, an auto-commit memory 1011, and a secondary powersupply 124. The storage device 102 may contain additional componentsthat are not shown in order to provide a simpler view of the storagedevice 102. Further, while the depicted components are part of thestorage device 102, in other embodiments, at least a portion of one ormore of the storage controller 104, the persistent data structure module1009, the auto-commit memory 1011, or the like may be located on thehost 114, as computer executable code, a device driver, an operatingsystem, or the like.

The non-volatile memory 110 stores data such that the data is retainedeven when the storage device 102 is not powered. Examples ofnon-volatile memory 110 include flash memory, nano random access memory(nano RAM or NRAM), nanocrystal wire-based memory, silicon-oxide basedsub-10 nanometer process memory, graphene memory,Silicon-Oxide-Nitride-Oxide-Silicon (SONOS), Resistive random-accessmemory (RRAM), programmable metallization cell (PMC),conductive-bridging RAM (CBRAM), magneto-resistive RAM (MRAM), dynamicRAM (DRAM), phase change RAM (PCM or PRAM), or other non-volatilesolid-state storage media. In other embodiments, the non-volatile memory110 may comprise magnetic media, optical media, or other types ofnon-volatile storage media. For example, in those embodiments, thenon-volatile storage device 102 may comprise a hard disk drive, anoptical storage drive, or the like.

While the non-volatile memory 110 is referred to herein as “memorymedia,” in various embodiments, the non-volatile memory 110 may moregenerally comprise a non-volatile recording media capable of recordingdata, the non-volatile recording media may be referred to as anon-volatile memory media, a non-volatile storage media, or the like.Further, the non-volatile storage device 102, in various embodiments,may comprise a non-volatile recording device, a non-volatile memorydevice, a non-volatile storage device, or the like.

The storage device 102 also includes a storage controller 104 thatcoordinates the storage and retrieval of data in the non-volatile memory110. The storage controller 104 may use one or more indexes to locateand retrieve data, and perform other operations on data stored in thestorage device 102. For example, the storage controller 104 may includea groomer for performing data grooming operations such as garbagecollection.

As shown, the storage device 102, in certain embodiments, implements awrite data pipeline 106 and a read data pipeline 108, an example ofwhich is described in greater detail below with regard to FIG. 3. Thewrite data pipeline 106 may perform certain operations on data as thedata is transferred from the host 114 into the non-volatile memory 110.These operations may include, for example, error correction code (ECC)generation, encryption, compression, and others. The read data pipeline108 may perform similar and potentially inverse operations on data thatis being read out of non-volatile memory 110 and sent to the host 114.

The storage device 102 also includes a secondary power supply 124 thatprovides power in the event of a complete or partial power disruptionresulting in the storage device 102 not receiving enough electricalpower over the primary power connection 130. A power disruption is anyevent that unexpectedly causes the storage device 102 to stop receivingpower over the primary power connection 130, or causes a significantreduction in the power received by the storage device 102 over theprimary power connection 130. A significant reduction in power, in oneembodiment, includes the power falling below a predefined threshold. Thepredefined threshold, in a further embodiment, is selected to allow fornormal fluctuations in the level of power from the primary powerconnection 130. For example, the power to a building where the host 114and the storage device 102 may go out. A user action (such as improperlyshutting down the host 114 providing power to the storage device 102), afailure in the primary power connection 130, or a failure in the primarypower supply may cause the storage device 102 to stop receiving power.Numerous, varied power disruptions may cause unexpected power loss forthe storage device 102.

The secondary power supply 124 may include one or more batteries, one ormore capacitors, a bank of capacitors, a separate connection to a powersupply, or the like. In one embodiment, the secondary power supply 124provides power to the storage device 102 for at least a power hold-uptime during a power disruption or other reduction in power from theprimary power connection 130. The secondary power supply 124, in afurther embodiment, provides a power hold-up time long enough to enablethe storage device 102 to flush data that is not in non-volatile memory110 into the non-volatile memory 110. As a result, the storage device102 can preserve the data that is not permanently stored in the storagedevice 102 before the lack of power causes the storage device 102 tostop functioning. In certain implementations, the secondary power supply124 may comprise the smallest capacitors possible that are capable ofproviding a predefined power hold-up time to preserve space, reducecost, and simplify the storage device 102. In one embodiment, one ormore banks of capacitors are used to implement the secondary powersupply 124 as capacitors are generally more reliable, require lessmaintenance, and have a longer life than other options for providingsecondary power.

In one embodiment, the secondary power supply 124 is part of anelectrical circuit that automatically provides power to the storagedevice 102 upon a partial or complete loss of power from the primarypower connection 130. Similarly, the system 100 may be configured toautomatically accept or receive electric power from the secondary powersupply 124 during a partial or complete power loss. For example, in oneembodiment, the secondary power supply 124 may be electrically coupledto the storage device 102 in parallel with the primary power connection130, so that the primary power connection 130 charges the secondarypower supply 124 during normal operation and the secondary power supply124 automatically provides power to the storage device 102 in responseto a power loss. In one embodiment, the system 100 further includes adiode or other reverse current protection between the secondary powersupply 124 and the primary power connection 130, to prevent current fromthe secondary power supply 124 from reaching the primary powerconnection 130. In another embodiment, the auto-commit memory 1011 mayenable or connect the secondary power supply 124 to the storage device102 using a switch or the like in response to reduced power from theprimary power connection 130.

An example of data that is not yet in the non-volatile memory 110 mayinclude data that may be held in volatile memory as the data movesthrough the write data pipeline 106. If data in the write data pipeline106 is lost during a power outage (i.e., not written to non-volatilememory 110 or otherwise permanently stored), corruption and data lossmay result.

In certain embodiments, the storage device 102 sends an acknowledgementto the host 114 at some point after the storage device 102 receives datato be stored in the non-volatile memory 110. The write data pipeline106, or a sub-component thereof, may generate the acknowledgement. It isadvantageous for the storage device 102 to send the acknowledgement assoon as possible after receiving the data.

In certain embodiments, the write data pipeline 106 sends theacknowledgement before data is actually stored in the non-volatilememory 110. For example, the write data pipeline 106 may send theacknowledgement while the data is still in transit through the writedata pipeline 106 to the non-volatile memory 110. In such embodiments,it is highly desirable that the storage device 102 flush all data forwhich the storage controller 104 has sent an acknowledgement to thenon-volatile memory 110 before the secondary power supply 124 losessufficient power in order to prevent data corruption and maintain theintegrity of the acknowledgement sent.

In addition, in certain embodiments, some data within the write datapipeline 106 may be corrupted as a result of the power disruption. Apower disruption may include a power failure as well as unexpectedchanges in power levels supplied. The unexpected changes in power levelsmay place data that is in the storage device 102, but not yet innon-volatile memory 110, at risk. Data corruption may begin to occurbefore the auto-commit memory 1011 is even aware (or notified) thatthere has been a disruption in power.

For example, the PCI-e specification indicates that, in the event that apower disruption is signaled, data should be assumed corrupted and notstored in certain circumstances. Similar potential corruption may occurfor storage devices 102 connected to hosts 114 using other connectiontypes, such as PCI, serial advanced technology attachment (serial ATA orSATA), parallel ATA (PATA), small computer system interface (SCSI), IEEE1394 (FireWire), Fiber Channel, universal serial bus (USB), PCIe-AS, orthe like. A complication may arise when a power disruption occurs(meaning that data received from that point to the present time may bepresumed corrupt), a period of time passes, the disruption is sensed andsignaled, and the auto-commit memory 1011 receives the signal andbecomes aware of the power disruption. The lag between the powerdisruption occurring and the auto-commit memory 1011 discovering thepower disruption can allow corrupt data to enter the write data pipeline106. In certain embodiments, this corrupt data should be identified andnot stored to the non-volatile memory 110. Alternately, this corruptdata can be stored in the non-volatile memory 110 and marked as corruptas described below. For simplicity of description, identifying corruptdata and not storing the data to the non-volatile memory 110 will beprimarily used to describe the functions and features herein.Furthermore, the host 114 should be aware that this data was not stored,or alternatively data for which integrity is a question is notacknowledged until data integrity can be verified. As a result, corruptdata should not be acknowledged.

The storage device 102 also includes the auto-commit memory 1011. Incertain embodiments, the auto-commit memory 1011 is in communicationwith, managed by, or at least partially integrated with the storagecontroller 104. The auto-commit memory 1011 may, for instance, cooperatewith a software driver and/or firmware for the storage device 102. Inone embodiment, at least a portion of the auto-commit memory 1011 isimplemented on the storage device 102, so that the auto-commit memory1011 continues to function during a partial or complete power loss usingpower from the secondary power supply 124, even if the host 114 is nolonger functioning.

In one embodiment, the auto-commit memory 1011 initiates a power lossmode in the storage device 102 in response to a reduction in power fromthe primary power connection 130. During the power loss mode, theauto-commit memory 1011, in one embodiment flushes data that is in thestorage device 102 that is not yet stored in non-volatile memory 110into the non-volatile memory 110. In particular embodiments, theauto-commit memory 1011 flushes the data that has been acknowledged andis in the storage device 102 that is not yet stored in non-volatilememory 110 into the non-volatile memory 110. In certain embodiments,described below, the auto-commit memory 1011 may adjust execution ofdata operations on the storage device 102 to ensure that essentialoperations complete before the secondary power supply 124 losessufficient power to complete the essential operations, i.e. during thepower hold-up time that the secondary power supply 124 provides.

In certain embodiments, the essential operations comprise thoseoperations for data that has been acknowledged as having been stored,such as acknowledged write operations. In other embodiments, theessential operations comprise those operations for data that has beenacknowledged as having been stored and erased. In other embodiments, theessential operations comprise those operations for data that have beenacknowledged as having been stored, read, and erased. The auto-commitmemory 1011 may also terminate non-essential operations to ensure thatthose non-essential operations do not consume power unnecessarily and/ordo not block essential operations from executing; for example, theauto-commit memory 1011 may terminate erase operations, read operations,unacknowledged write operations, and the like.

In one embodiment, terminating non-essential operations preserves powerfrom the secondary power supply 124, allowing the secondary power supply124 to provide the power hold-up time. In a further embodiment, theauto-commit memory 1011 quiesces or otherwise shuts down operation ofone or more subcomponents of the storage device 102 during the powerloss mode to conserve power from the secondary power supply 124. Forexample, in various embodiments, the auto-commit memory 1011 may quiesceoperation of the read data pipeline 108, a read direct memory access(DMA) engine, and/or other subcomponents of the storage device 102 thatare associated with non-essential operations.

The auto-commit memory 1011 may also be responsible for determining whatdata was corrupted by the power disruption, preventing the corrupt datafrom being stored in non-volatile memory 110, and ensuring that the host114 is aware that the corrupted data was never actually stored on thestorage device 102. This prevents corruption of data in the storagedevice 102 resulting from the power disruption.

In one embodiment, the system 100 includes a plurality of storagedevices 102. The auto-commit memory 1011, in one embodiment, managespower loss modes for each storage device 102 in the plurality of storagedevices 102, providing a system-wide power loss mode for the pluralityof storage devices 102. In a further embodiment, each storage device 102in the plurality of storage devices 102 includes a separate auto-commitmemory 1011 that manages a separate power loss mode for each individualstorage device 102. The auto-commit memory 1011, in one embodiment, mayquiesce or otherwise shut down one or more storage devices 102 of theplurality of storage devices 102 to conserve power from the secondarypower supply 124 for executing essential operations on one or more otherstorage devices 102.

In one embodiment, the system 100 includes one or more adapters forproviding electrical connections between the host 114 and the pluralityof storage devices 102. An adapter, in various embodiments, may includea slot or port that receives a single storage device 102, an expansioncard or daughter card that receives two or more storage devices 102, orthe like. For example, in one embodiment, the plurality of storagedevices 102 may each be coupled to separate ports or slots of the host114. In another example embodiment, one or more adapters, such asdaughter cards or the like, may be electrically coupled to the host 114(i.e. connected to one or more slots or ports of the host 114) and theone or more adapters may each provide connections for two or morestorage devices 102.

In one embodiment, the system 100 includes a circuit board, such as amotherboard or the like, that receives two or more adapters, such asdaughter cards or the like, and each adapter receives two or morestorage devices 102. In a further embodiment, the adapters are coupledto the circuit board using PCI-e slots of the circuit board and thestorage devices 102 are coupled to the adapters using PCI-e slots of theadapters. In another embodiment, the storage devices 102 each comprise adual in-line memory module (DIMM) of non-volatile solid-state storage,such as Flash memory, or the like. In one embodiment, the circuit board,the adapters, and the storage devices 102 may be external to the host114, and may include a separate primary power connection 130. Forexample, the circuit board, the adapters, and the storage devices 102may be housed in an external enclosure with a power supply unit (PSU)and may be in communication with the host 114 using an external bus suchas eSATA, eSATAp, SCSI, FireWire, Fiber Channel, USB, PCIe-AS, or thelike. In another embodiment, the circuit board may be a motherboard ofthe host 114, and the adapters and the storage devices 102 may beinternal storage of the host 114.

In view of this disclosure, one of skill in the art will recognize manyconfigurations of adapters and storage devices 102 for use in the system100. For example, each adapter may receive two storage devices 102, fourstorage devices 102, or any number of storage devices. Similarly, thesystem 100 may include one adapter, two adapters, three adapters, fouradapters, or any supported number of adapters. In one exampleembodiment, the system 100 includes two adapters and each adapterreceives four storage devices 102, for a total of eight storage devices102.

In one embodiment, the secondary power supply 124 provides electricpower to each of a plurality of storage devices 102. For example, thesecondary power supply 124 may be disposed in a circuit on a maincircuit board or motherboard and may provide power to several adapters.In a further embodiment, the system 100 includes a plurality ofsecondary power supplies that each provide electric power to a subset ofa plurality of storage devices 102. For example, in one embodiment, eachadapter may include a secondary power supply 124 for storage devices 102of the adapter. In a further embodiment, each storage device 102 mayinclude a secondary power supply 124 for the storage device 102. In viewof this disclosure, one of skill in the art will recognize differentarrangements of secondary power supplies 124 for providing power to aplurality of storage devices 102.

The systems, methods, and apparatus described above may be leveraged toimplement an auto-commit memory capable of implementing memory semanticwrite operations (e.g., persistent writes) at CPU memory writegranularity and speed. By guaranteeing that certain commit actions forthe write operations will occur, even in the case of a power failure orother restart event, in certain embodiments, volatile memory such asDRAM, SRAM, BRAM, or the like, may be used as, considered, orrepresented as non-volatile.

The auto-commit memory described herein, may be configured to ensure orguarantee that data is preserved or persisted, even while the data isstored in a volatile auto-commit memory buffer. The volatile auto-commitmemory buffers, elements, modules, or devices described herein, may bearmed or associated with auto-commit metadata defining a commit actionfor the auto-commit memory module 1011 to perform in response to atrigger. A trigger, a commit trigger, a trigger event, a commit event,or the like for the auto-commit memory module 1011, as used herein, maycomprise an occurrence, a system state, a condition, or the like, inresponse to which the auto-commit memory module 1011 is configured toperform one or more commit actions, such as flushing or preserving datafrom a volatile memory to the non-volatile memory medium 110. Theauto-commit memory module 1011, in certain embodiments, may flush,stream, copy, transfer, or destage data from an auto-commit memorybuffer without regard to any single specific trigger event. For example,destaging data from an auto-commit memory buffer to a non-volatilememory medium 110 is described below with regard to the destage module1908 of FIG. 10.

In certain embodiments, a trigger for the auto-commit memory module 1011may comprise a non-failure, non-power-loss, and/or non-restart eventduring routine runtime of the system 100, such as an auto-commit memorybuffer becoming full, receiving a destage request, or the like. In otherembodiments, a trigger may comprise a failure condition, a power-losscondition, or other restart event. A restart event, as used herein,comprises an intentional or unintentional loss of power to at least aportion of the host computing device and/or a non-volatile storagedevice. A restart event may comprise a system reboot, reset, or shutdownevent; a power fault, power loss, or power failure event; or anotherinterruption or reduction of power. By guaranteeing certain commitactions, the auto-commit memory may allow storage clients to resumeexecution states, even after a restart event, may allow the storageclients to persist different independent data sets, or the like.

As used herein, the term “memory semantic operations,” or moregenerally, “memory operations,” refers to operations having agranularity, synchronicity, and access semantics of volatile memoryaccesses, using manipulatable memory pointers, or the like. Memorysemantic operations may include, but are not limited to: load, store,peek, poke, write, read, set, clear, and so on. Memory semanticoperations may operate at a CPU-level of granularity (e.g., singlebytes, words, cache lines, or the like), and may be synchronous (e.g.,the CPU waits for the operation to complete). In certain embodiments,providing access at a larger sized granularity, such as cache lines, mayincrease access rates, provide more efficient write combining, or thelike than smaller sized granularity access.

The ACM 1011 may be available to computing devices and/or applications(both local and remote) using one or more of a variety of memory mappingtechnologies, including, but not limited to, memory mapped I/O (MMIO),port I/O, port-mapped IO (PMIO), Memory mapped file I/O, and the like.For example, the ACM 1011 may be available to computing devices and/orapplications (both local and remote) using a PCI-e Base Address Register(BAR), or other suitable mechanism. ACM 1011 may also be directlyaccessible via a memory bus of a CPU, using an interface such as adouble data rate (DDR) memory interface, HyperTransport, QuickPathInterconnect (QPI), or the like. Accordingly, the ACM 1011 may beaccessible using memory access semantics, such as CPU load/store, directmemory access (DMA), 3^(rd) party DMA, remote DMA (RDMA), atomic testand set, and so on. The direct, memory semantic access to the ACM 1011disclosed herein allows many of the system and/or virtualization layercalls typically required to implement committed operations to bebypassed, (e.g., call backs via asynchronous Input/Output interfaces maybe bypassed). In some embodiments, an ACM 1011 may be mapped to one ormore virtual ranges (e.g., virtual BAR ranges, virtual memory addresses,or the like). The virtual mapping may allow multiple computing devicesand/or applications to share a single ACM address range 1021 (e.g.,access the same ACM simultaneously, within different virtual addressranges). An ACM 1011 may be mapped into an address range of a physicalmemory address space addressable by a CPU so that the CPU may useload/store instructions to read and write data directly to the ACM 1011using memory semantic accesses. A CPU, in a further embodiment, may mapthe physically mapped ACM 1011 into a virtual memory address space,making the ACM 1011 available to user-space processes or the like asvirtual memory.

The ACM 1011 may be pre-configured to commit its contents upon detectionof a restart condition (or other pre-determined triggering event) and,as such, operations performed on the ACM 1011 may be viewed as being“instantly committed.” For example, an application may perform a“write-commit” operation on the ACM 1011 using memory semantic writesthat operate at CPU memory granularity and speed, without the need forseparate corresponding “commit” commands, which may significantlyincrease the performance of applications affected by write-commitlatencies. As used herein, a write-commit operation is an operation inwhich an application writes data to a memory location (e.g., using amemory semantic access), and then issues a subsequent commit command tocommit the operation (e.g., to persistent storage or other commitmechanism).

Applications whose performance is based on write-commit latency, thetime delay between the initial memory write and the subsequentpersistent commit operation, typically attempt to reduce this latency byleveraging a virtual memory system (e.g., using a memory backed file).In this case, the application performs high-performance memory semanticwrite operations in system RAM, but, in order to commit the operations,must perform subsequent “commit” commands to persist each writeoperation to the backing file (or other persistent storage).Accordingly, each write-commit operation may comprise its own separatecommit command. For example, in a database logging application, each logtransaction must be written and committed before a next transaction islogged. Similarly, messaging systems (e.g., store and forward systems)must write and commit each incoming message, before receipt of themessage can be acknowledged. The write-commit latency, therefore,comprises a relatively fast memory semantic write followed by a muchslower operation to commit the data to persistent storage. Write-commitlatency may include several factors including, access times topersistent storage, system call overhead (e.g., translations between RAMaddresses, backing store LBA, etc.), and so on. Examples of applicationsthat may benefit from reduced write-commit latency include, but are notlimited to: database logging applications, file system logging,messaging applications (e.g., store and forward), semaphore primitives,and so on.

The systems, apparatus, and methods for persistent data structures usingauto-commit memory disclosed herein may be used to significantlyincrease the performance of write-commit latency bound applications byproviding direct access to a memory region at any suitable level ofaddressing granularity including byte level, page level, cache-linelevel, or other memory region level, that is guaranteed to be committedin the event of a system failure or other restart event, without theapplication issuing a commit command. Accordingly, the write-commitlatency of an application may be reduced to the latency of a memorysemantic access (a single write over a system bus).

The persistent data structure module 1009, in certain embodiments, mayuse or cooperate with the auto-commit memory 1011, as described herein,to provide persistent data structures to clients (e.g., an operatingsystem, virtual operating platform, guest operating system, application,database system, process, thread, entity, utility, user, or the like)with many of the benefits and speed of volatile memory and thepersistence of the non-volatile memory medium 110.

A data structure, as used herein, comprises an organized arrangement,group, or set of data. A data structure may be organized according to apredefined pattern or schema, may comprise metadata such as pointers,sequence numbers, labels, identifiers, or the like to facilitateorganization of and access to the included data. Data structures mayinclude, but are not limited to, a log (e.g., a sequential log, atransaction log, an application log), a queue (e.g., afirst-in-first-out or FIFO queue, a buffer), a stack (e.g. alast-in-first-out or LIFO stack), a tree (e.g., a binary tree, B-tree,B+ tree, B*tree, ternary tree, K-ary tree, space-partitioning tree,decision tree), a linked-list (e.g., singly linked list, doubly linkedlist, self-organizing list, doubly connected edge list), a hash (e.g., ahash list, hash table, hash tree, hash array), an array (e.g., a table,map, bit array, bit field, bitmap, matrix, sparse array), a heap (e.g.,a binary heap, binomial heap, Fibonacci heap, ternary heap, D-ary heap),a graph (e.g., directed graph, directed acyclic graph, binary decisiondiagram, graph-structured stack, multigraph, hypergraph, adjacencylist), or other data structure.

One example of a data structure is a transaction log or TLOG. Atransaction log (e.g., a transaction journal, a database log, a binarylog, an audit trail, a sequential log, an application log), in certainembodiments, includes sequential, historical, or chronological entries,such as a history or list of updates made to a database or databasetable, transactions executed by a database or other application, or thelike. A transaction log may include enough information regarding eachtransaction to either rollback or undo the transaction, or to redo orreapply the transaction. In addition to or instead of being storedsequentially or chronologically, in certain embodiments, a transactionlog may include sequence information for each entry or transaction, suchas a timestamp, a sequence number, a link to a previous or next entry,or the like. A transaction log may also include other types of metadata,such as a transaction identifier (e.g., a reference to a databasetransaction that generated the log record), a type (e.g., a labeldescribing the type of database log record), or the like. While apersistent transaction log is primarily described herein with regard tothe persistent data structure module 1009, the description is equallyapplicable to other types of data structures, such as the example datastructures listed above.

The persistent data structure module 1009 may provide an interface, suchas an application programming interface (API), shared library, hardwareinterface, a communications bus, one or more JO control (IOCTL)commands, or the like, over which a client may create, update, delete,or otherwise access one or more types of persistent data structures. Adata structure, as used herein, is persistent if the data structureremains accessible to a client in some form after a restart event, whichmay be ensured or guaranteed by the auto-commit memory 1011, asdescribed herein. The persistent data structure module 1009 mayassociate a persistent logical identifier with a persistent datastructure, which a client may use to access the persistent datastructure both before and after a restart event. For example, thepersistent data structure module 1009 may cooperate with a file systemmodule 1558 as described below with regard to FIG. 6 to provide accessto a persistent data structure as a file system file with a filename, afilename and an offset, or the like. In other embodiments, a persistentlogical identifier may comprise a logical unit number (LUN) identifier(ID) from a LUN namespace, a LUN ID and an offset, a logical identifierfor a persistent memory namespace for the ACM 1011 as described below, alogical block address (LBA) or LBA range from a namespace of thenon-volatile memory device 102, or another persistent logicalidentifier.

To make efficient use of the ACM 1011, which may have a smaller storagecapacity than the non-volatile memory medium 110, and to provide theaccess speed of volatile memory and the persistence of the non-volatilememory medium 110, as a client writes data to a data structure (e.g., inthe foreground) at an input rate, the persistent data structure module1009 may cooperate with the ACM 1011 to destage, copy, transfer,migrate, and/or move data from ACM buffers of the ACM 1011 to thenon-volatile memory medium 110 (e.g., in the background) at a transferrate that matches or exceeds the input rate over time, so that the datadoes not overrun the one or more ACM buffers allocated to the datastructure. The persistent data structure module 1009, in one embodiment,may block, delay, throttle, govern, or otherwise limit the input rate atwhich a client writes data to a data structure. In this manner, thepersistent data structure module 1009 may mask or hide the ACM 1011and/or non-volatile memory medium 110 from a client such that the clientperceives the access speed and benefits of the ACM 1011 and thepersistence of the non-volatile memory medium 110, without being awareof the complexities of the tiered architecture that the persistent datastructure module 1009 uses to provide these benefits.

The persistent data structure module 1009, in certain embodiments, mayenforce one or more rules for a data structure. For example, eachdifferent type of data structure may be defined or structured by a setof one or more rules, restrictions, definitions, or the like. The rulesmay define one or more allowed or acceptable data operations for a datastructure. For a transaction log, the rules may include that entriesmust be sequential, that data entries may not be overwritten or updatedonce written, or the like. Different types of data structures may havedifferent rules. For example, a queue may have a strict FIFO rule, astack may have a strict LIFO rule, a tree may have a rule defining astrict order or hierarchy for data entries or nodes, a data structuremay have a rule requiring certain data types or required fields orentries, or the like. In certain embodiments, by providing an interfacethat enforces one or more rules for a data structure, the persistentdata structure module 1009 may prevent an application or other clientfrom inadvertently or accidently overwriting or otherwise violating theintegrity of a persistent data structure, ensuring that the persistentdata structure satisfies the data structure's strict definition, or thelike. Because the persistent data structure module 1009 provides datastructures that are non-volatile or persistent, errors in data structureintegrity (e.g., an overwritten data structure, an improper entry in adata structure, or the like) would otherwise persist after a restartevent or reboot, and would not be cleared or reset as would errors in avolatile data structure.

The persistent data structure module 1009, in certain embodiment, mayprovide an interface or library that integrates with and/or provides anoperating system, a file system, one or more applications or otherclients, or the like access to the hardware capabilities of the ACM 1011and/or the non-volatile memory medium 110 in a substantially transparentmanner, thereby providing persistent data structures accessible via alibrary, a filename or other persistent logical identifier, or the like.Because the persistent data structure module 1009 manages the tieredhierarchy of the ACM 1011, the non-volatile memory medium 110 (e.g., thestorage management layer described below), a file system (e.g., the filesystem module 1558 described below), in one embodiment, the persistentdata structure module 1009 may provide the benefits of the ACM 1011 forpersistent data structures, even with a small amount of volatile memoryfor the ACM 1011 (e.g., ACM buffers) relative to storage capacity of thenon-volatile memory medium 110.

In certain embodiments, the persistent data structure module 1009 mayprovide substantially transparent integration of persistent datastructures with a file system. For example, a client may access apersistent data structure using file system semantics, as a file with afilename, using a filename and an offset, or the like, while thepersistent data structure module 1009 manages the transfer of data ofthe data structure between the ACM buffers (e.g., volatile memory,volatile memory buffers, volatile memory modules, volatile memoryelements, volatile memory pages) of the ACM 1011 and the non-volatilememory medium 110, enforces one or more rules for the data structure(e.g., prevents a file for a data structure from being overwritten,ensures a file for a data structure is append-only, ensures entries of afile for a data structure are sequential, or the like), so that theclient is spared such responsibilities. In this manner, an applicationor other client may receive the benefits of the persistent datastructure module 1009 and/or the ACM 1011 for persistent data structureswhile using a standard library, file system I/O, or other interface.

FIG. 2 is a block diagram of a system 1000 comprising one embodiment ofa persistent data structure module 1009 and an auto-commit memory (ACM)1011. As used herein, an auto-commit memory comprises low-latency, highreliability memory media, exposed to the persistent data structuremodule 1009 and/or other ACM users for direct memory semantic access, ata memory semantic access and address granularity level of at least bytelevel, combined with logic and components together configured to restorethe same state of data stored in the ACM 1011 that existed prior to therestart event and the same level of memory semantic access to datastored in the auto-commit memory after a restart event. In certainembodiments, the ACM 1011 guarantees that data stored in the ACM 1011will be accessible after a restart event. The ACM 1011, in oneembodiment, comprises a volatile memory media coupled to a controller,logic, and other components that commit data to a non-volatile storagemedium when necessary or when directed by an ACM user. In a furtherembodiment, the ACM 1011 may include a natively non-volatile storagemedium such as phase change memory (PCM or PRAM), and a triggered commitaction may process data on the non-volatile storage medium in responseto a restart event such that the data remains available to an owner ofthe data after the restart event.

Accordingly, when data is written to the ACM 1011, it may not initiallybe “committed” per se (is not necessarily stored on a persistent memorymedia and/or state); rather, a pre-configured process is setup topreserve the ACM data and its state, if a restart event occurs while theACM data is stored in the ACM 1011. The pre-configuring of this restartsurvival process is referred to herein as “arming.” The ACM 1011 may becapable of performing the pre-configured commit action autonomously andwith a high degree of assurance, despite the system 1000 experiencingfailure conditions or another restart event. As such, an entity thatstores data on the ACM 1011 may consider the data to be “instantaneouslycommitted” or safe from loss or corruption, at least as safe as if thedata were stored in a non-volatile storage device such as a hard diskdrive, tape storage media, or the like.

In embodiments where the ACM 1011 comprises a volatile memory media, theACM 1011 may make the volatile memory media appear as a non-volatilememory, may present the volatile memory as a non-volatile medium, or thelike, because the ACM 1011 preserves data, such as ACM data and/or ACMmetadata 1015, across system restart events. The ACM 1011 may allow avolatile memory media to be used as a non-volatile memory media bydetermining that a trigger event, such as a restart or failurecondition, has occurred, copying the contents of the volatile memorymedia to a non-volatile memory media during a hold-up time after thetrigger event, and copying the contents back into the volatile memorymedia from the non-volatile memory media after the trigger event isover, power has been restored, the restart event has completed, or thelike.

In one embodiment, the ACM 1011 is at least byte addressable. A memorymedia of the ACM 1011, in certain embodiments, may be natively byteaddressable, directly providing the ACM 1011 with byte addressability.In another embodiment, a memory media of the ACM 1011 is not nativelybyte addressable, but a volatile memory media of the ACM 1011 isnatively byte addressable, and the ACM 1011 writes or commits thecontents of the byte addressable volatile memory media to the non-byteaddressable memory media of the ACM 1011 in response to a trigger event,so that the volatile memory media renders the ACM 1011 byte addressable.

The ACM 1011 may be accessible to one or more computing devices, such asthe host 1014. As used herein a computing device (such as the host 1014)refers to a computing device capable of accessing an ACM. The host 1014may be a computing device that houses the ACM 1011 as a peripheral; theACM 1011 may be attached to a system bus 1040 of the host 1014; the ACM1011 may be in communication with the host 1014 over a data network;and/or the ACM 1011 may otherwise be in communication with the host1014. The host 1014, in certain embodiments, may access the ACM 1011hosted by another computing device. The access may be implemented usingany suitable communication mechanism, including, but not limited to: CPUprogrammed 10 (CPIO), port-mapped JO (PMIO), memory-mapped JO (MMIO), aBlock interface, a PCI-e bus, Infiniband, RDMA, or the like. The host1014 may comprise one or more ACM users 1016. As used herein, an ACMuser 1016 refers to any operating system (OS), virtual operatingplatform (e.g., an OS with a hypervisor), a guest OS, application,process, thread, entity, utility, user, or the like, that is configuredto access the ACM 1011.

The ACM 1011 may be physically located at one or more levels of the host1014. In one embodiment, the ACM 1011 may be connected to a PCI-e busand may be accessible to the host 1014 with MMIO. In another embodiment,the ACM 1011 may be directly accessible to a CPU of the host 1014 via amemory controller. For example, the ACM 1011 may be directly attached toand/or directly (e.g., Quick Path Interconnect (QPI)) in communicationwith a CPU of the host 1014 or the like. Volatile media of the ACM 1011and non-volatile backing media of the ACM 1011, in certain embodiments,may not be physically co-located within the same apparatus, but may bein communication over a communications bus, a data network, or the like.In other embodiments, as described below, hardware components of the ACM1011 may be tightly coupled, and integrated in a single physicalhardware apparatus. Volatile memory media and/or non-volatile memorymedia of the ACM 1011, in one embodiment, may be integrated with, or mayotherwise cooperate with, a CPU cache hierarchy of the host 1014, totake advantage of CPU caching technologies such as write combining orthe like.

One or more ACM buffers 1013, in certain embodiments, may be mapped intoan address range of a physical memory address space addressable by aCPU, a kernel, or the like of the host device 1014, such as the memorysystem 1018 described below. For example, one or more ACM buffers 1013may be mapped as directly attached physical memory, as MMIO addressablephysical memory over a PCI-e bus, or otherwise mapped as one or morepages of physical memory. At least a portion of the physically mappedACM buffers 1013, in a further embodiment, may be mapped into a virtualmemory address space, accessible to user-space processes or the like asvirtual memory.

Allowing ACM users 1016 to directly address the ACM buffers 1013, incertain embodiments, bypasses one or more layers of the traditionaloperating system memory stack of the host device 1014, providing directload/store operation access to kernel-space and/or user-spaceapplications. An operating system, using a kernel module, an applicationprogramming interface, the storage management layer (SML) 1050 describedbelow, or the like, in one embodiment, maps and unmaps ACM buffers 1013to and from the memory system 1018 for one or more ACM users 1016, andthe ACM users 1016 may directly access an ACM buffer 1013 once theoperating system maps the ACM buffer 1013 into the memory system 1018.In a further embodiment, the operating system may also service systemflush calls for the ACM buffers 1013, or the like.

The storage management module 1050 and/or the SML API 1019 describedbelow, in certain embodiments, provide an interface for ACM users 1016,an operating system, and/or other entities to request certain ACMfunctions, such as a map function, an unmap function, a flush function,and/or other ACM functions. To perform a flush operation in response toa flush request, the ACM 1011 may perform a commit action for each ACMbuffer 1013 associated with the flush request. Each ACM buffer 1013 iscommitted as indicated by the ACM metadata 1015 of the associated ACMbuffer 1013. A flush function, in various embodiments, may be specificto one or more ACM buffers 1013, system-wide for all ACM buffers 1013,or the like. In one embodiment, a CPU, an operating system, or the likefor the host 1014 may request an ACM flush operation in response to, oras part of a CPU cache flush, a system-wide data flush for the host1014, or another general flush operation.

An ACM user 1016, an operating system, or the like may request a flushoperation to maintain data consistency prior to performing a maintenanceoperation, such as a data snapshot or a backup, to commit ACM data priorto reallocating an ACM buffer 1013, to prepare for a scheduled restartevent, or for other circumstances where flushing data from an ACM buffer1013 may be beneficial. An ACM user 1016, an operating system, or thelike, in certain embodiments, may request that the ACM 1011 map and/orunmap one or more ACM buffers 1013 to perform memory management for theACM buffers 1013; to reallocate the ACM buffers 1013 betweenapplications or processes; to allocate ACM buffers 1013 for new data,applications, or processes; to transfer use of the ACM buffers 1013 to adifferent host 1014 (in shared ACM 1011 embodiments); or to otherwisemanipulate the memory mapping of the ACM buffers 1013. In anotherembodiment, the storage management module 1050 may dynamically allocate,map, and/or unmap ACM buffers 1013 using a resource management agent asdescribed below.

Since the ACM 1011 is guaranteed to auto-commit the data stored thereonin the event of a trigger event, the host 1014 (or ACM user 1016) mayview data written to the ACM 1011 as being instantaneously “committed”or non-volatile, as the host 1014 or ACM user 1016 may access the databoth before and after the trigger event. Advantageously, while therestart event may cause the ACM user 1016 to be re-started orre-initialized the data stored in the ACM 1011 is in the samestate/condition after the restart event as it was before the restartevent. The host 1014 may, therefore, write to the ACM 1011 using memorywrite semantics (and at CPU speeds and granularity), without the needfor explicit commit commands by relying on the pre-configured trigger ofthe ACM 1011 to commit the data in the event of a restart (or othertrigger event).

The ACM 1011 may comprise a plurality of auto-commit buffers 1013, eachcomprising respective ACM metadata 1015. As discussed below, the ACMmetadata 1015 may include data to facilitate committing of ACM data inresponse to a triggering event for the auto-commit buffer 1013, such asa logical identifier for data in the ACM buffer 1013, an identifier of acommit agent 1020, instructions for a commit process or other processingprocedure, security data, or the like. The auto-commit buffers 1013 maybe of any suitable size, from a single sector, page, byte, or the like,to a virtual or logical page size (e.g., 80 to 400 kb). The size of theauto-commit buffers 1013 may be adapted according to the storagecapacity of the underlying non-volatile storage media, and or hold-uptime available from the secondary power supply 1024.

In one embodiment, the ACM 1011 may advertise or present to the host1014, to ACM users 1016, or the like, a storage capacity of the ACMbuffers 1013 that is larger than an actual storage capacity of memory ofthe ACM buffers 1013. To provide the larger storage capacity, the ACM1011 may dynamically map and unmap ACM buffers 1013 to the memory system1018 and to the non-volatile backing memory of the ACM 1011, such as thenon-volatile memory 110 described above. For example, the ACM 1011 mayprovide virtual address ranges for the ACM buffers 1013, and demand pagedata and/or ACM buffers 1013 to the non-volatile memory 110 as ACMbuffer 1013 accesses necessitate. In another embodiment, for ACM buffers1013 that are armed to commit to one or more predefined LBAs of thenon-volatile memory 110, the ACM 1011 may dynamically move the ACM dataand ACM metadata 1015 from the ACM buffers 1013 to the associated LBAsof the non-volatile memory 110, freeing storage capacity of the ACMbuffers 1013 to provide a larger storage capacity. The ACM 1011 mayfurther return the ACM data and ACM metadata 1015 back to one or moreACM buffers 1013 as ACM buffers become available, certain addressesoutside the data of currently loaded ACM buffers 1013 is requested, orthe like, managing storage capacity of the ACM buffers 1013.

The ACM 1011 is pre-configured or “armed” to implement one or more“triggered commit actions” in response to a restart condition (or other,pre-determined condition). As used herein, a restart condition or eventmay include, but is not limited to a software or hardwareshutdown/restart of a host 1014, a failure in a host 1014 computingdevice, a failure of a component of the host 1014 (e.g., failure of thebus 1040), a software fault (e.g., an fault in software running on thehost 1014 or other computing device), a loss of the primary powerconnection 1030, an invalid shutdown, or another event that may causethe loss of data stored in a volatile memory.

In one embodiment, a restart event comprises the act of the host 1014commencing processing after an event that can cause the loss of datastored within a volatile memory of the host 1014 or a component in thehost 1014. The host 1014 may commence/resume processing once the restartcondition or event has finished, a primary power source is available,and the like.

The ACM 1011 is configured to detect that a restart event/condition hasoccurred and/or respond to a restart event by initiating a recoverystage. During a recovery stage, the ACM 1011 may restore the data of theACM 1011 to the state prior to the restart event. Alternatively, or inaddition, during the recovery stage, the ACM 1011 may completeprocessing of ACM data or ACM metadata 1015 needed to satisfy aguarantee that data in the ACM 1011 is available to ACM users after therestart event. Alternatively, or in addition, during the recovery stage,the ACM 1011 may complete processing of ACM data or ACM metadata 1015needed to satisfy a guarantee that data in the ACM 1011 is committedafter the restart event. As used herein, “commit” means data in the ACM1011 is protected from loss or corruption even after the restart eventand is persisted as required per the arming information associated withthe data. In certain embodiments, the recovery stage includes processingACM data and ACM metadata 1015 such that the ACM data is persisted, eventhough the restart event occurred.

As used herein, a triggered commit action is a pre-configured commitaction that is armed to be performed by the ACM 1011 in response to atriggering event (e.g., a restart event, a flush command, or otherpre-determined event). In certain embodiments, the triggered commitaction persists at least enough ACM data and/or ACM metadata 1015 tomake data of the ACM 1011 available after a system restart, to satisfy aguarantee of the ACM 1011 that the data will be accessible to an ACMuser after a restart event, in certain embodiments, this guarantee issatisfied, at least in part, by committing and/or persisting data of theACM 1011 to non-volatile memory media. A triggered commit action may becompleted before, during, and/or after a restart event. For example, theACM 1011 may write ACM data and ACM metadata 1015 to a predefinedtemporary location in the non-volatile memory 110 during a hold-up timeafter a restart event, and may copy the ACM data back into the ACMbuffers 1013, to an intended location in the non-volatile memory 110, orperform other processing once the restart event is complete.

A triggered commit action may be “armed” when the ACM 1011 is requestedand/or a particular ACM buffer 1013 is allocated for use by a host 1014.In some embodiments, an ACM 1011 may be configured to implement atriggered commit action in response to other, non-restart conditions.For example, an operation directed to a particular logical address(e.g., a poke), may trigger the ACM 1011, a flush operation may triggerthe ACM 1011, or the like. This type of triggering may be used to committhe data of the ACM 1011 during normal operation (e.g., non-restart ornon-failure conditions).

The arming may occur when an auto-commit buffer 1013 is mapped into thememory system 1018 of the host 1014. Alternatively, arming may occur asa separate operation. As used herein, arming an auto-commit buffer 1013comprises performing the necessary configuration steps needed tocomplete the triggered action when the action is triggered. Arming mayinclude, for example, providing the ACM metadata 1015 to the ACM 1011 orthe like. In certain embodiments, arming further includes performing thenecessary configuration steps needed to complete a minimal set of stepsfor the triggered action, such that the triggered action is capable ofcompleting after a trigger event. In certain embodiments, arming furtherincludes verifying the arming data (e.g., verifying that the contents ofthe auto-commit buffer 1013, or portion thereof, can be committed asspecified in the ACM metadata 1015) and verifying that the ACM 1011 iscapable and configured to properly perform the triggered action withouterror or interruption.

The verification may ensure that once armed, the ACM 1011 can implementthe triggered commit action when required. If the ACM metadata 1015cannot be verified (e.g., the logical identifier or other ACM metadata1015 is invalid, corrupt, unavailable, or the like), the armingoperation may fail; memory semantic operations on the auto-commit buffer1013 may not be allowed unit the auto-commit buffer 1013 is successfullyarmed with valid ACM metadata 1015. For example, an auto-commit buffer1013 that is backed by a hard disk having a one-to-one mapping betweenLBA and physical address, may fail to arm if the LBA provided for thearming operation does not map to a valid (and operational) physicaladdress on the disk. Verification in this case may comprise querying thedisk to determine whether the LBA has a valid, corresponding physicaladdress and/or using the physical address as the ACM metadata 1015 ofthe auto-commit buffer 1013.

The armed triggered commit actions are implemented in response to theACM 1011 (or other entity) detecting and/or receiving notification of atriggering event, such as a restart condition. In some embodiments, anarmed commit action is a commit action that can be performed by the ACM1011, and that requires no further communication with the host 1014 orother devices external to the “isolation zone” of the ACM 1011(discussed below). Accordingly, the ACM 1011 may be configured toimplement triggered commit actions autonomously of the host 1014 and/orother components thereof. The ACM 1011 may guarantee that triggeredcommit actions can be committed without errors and/or despite externalerror conditions. Accordingly, in some embodiments, the triggered commitactions of the ACM 1011 do not comprise and/or require potentiallyerror-introducing logic, computations, and/or calculations. In someembodiments, a triggered commit action comprises committing data storedon the volatile ACM 1011 to a persistent storage location. In otherembodiments, a triggered commit action may comprise additionalprocessing of committed data, before, during, and/or after a triggeringevent, as described below. The ACM 1011 may implement pre-configuredtriggered commit actions autonomously; the ACM 1011 may be capable ofimplementing triggered commit actions despite failure or restartconditions in the host 1014, loss of primary power, or the like. The ACM1011 can implement triggered commit actions independently due to armingthe ACM 1011 as described above.

The ACM metadata 1015 for an ACM buffer 1013, in certain embodiments,identifies the data of the ACM buffer 1013. For example, the ACMmetadata 1015 may identify an owner of the data, may describe the dataitself, or the like. In one embodiment, an ACM buffer 1013 may havemultiple levels of ACM metadata 1015, for processing by multipleentities or the like. The ACM metadata 1015 may include multiple nestedheaders that may be unpackaged upon restart, and used by variousentities or commit agents 1020 to determine how to process theassociated ACM data to fulfill the triggered commit action as describedabove. For example, the ACM metadata 1015 may include block metadata,file metadata, application level metadata, process execution point orcallback metadata, and/or other levels of metadata. Each level ofmetadata may be associated with a different commit agent 1020, or thelike. In certain embodiments, the ACM metadata 1015 may include securitydata, such as a signature for an owner of the associated ACM data, apre-shared key, a nonce, or the like, which the ACM 1011 may use duringrecovery to verify that a commit agent 1020, an ACM user 1016, or thelike is authorized to access committed ACM metadata 1015 and/orassociated ACM data. In this manner, the ACM 1011 may prevent ownershipspoofing or other unauthorized access. In one embodiment, the ACM 1011does not release ACM metadata 1015 and/or associated ACM data until arequesting commit agent 1020, ACM user 1016, or the like provides validauthentication, such as a matching signature or the like.

One or more commit agents 1020, such as the commit management apparatus1122 described below with regard to FIG. 3, in certain embodiments,process ACM data based on the associated ACM metadata 1015 to execute atriggered commit action. A commit agent 1020, in various embodiments,may comprise software, such as a device driver, a kernel module, thestorage management module 1050, a thread, a user space application, orthe like, and/or hardware, such as the controller 1004 described below,that is configured to interpret ACM metadata 1015 and to process theassociated ACM data according to the ACM metadata 1015. In embodimentswith multiple commit agents 1020, the ACM metadata 1015 may identify oneor more commit agents 1020 to process the associated ACM data. The ACMmetadata 1015 may identify a commit agent 1020, in various embodiments,by identifying a program/function of the commit agent 1020 to invoke(e.g., a file path of the program), by including computer executablecode of the commit agent 1020 (e.g., binary code or scripts), byincluding a unique identifier indicating which of a set of registeredcommit agents 1020 to use, and/or by otherwise indicating a commit agent1020 associated with committed ACM metadata 1015. The ACM metadata 1015,in certain embodiments, may be a functor or envelope which contains theinformation, such as function pointer and bound parameters for a commitagent 1020, to commit the ACM data upon restart recovery.

In one embodiment, a primary commit agent 1020 processes ACM metadata1015, and hands-off or transfers ACM metadata 1015 and/or ACM data toone or more secondary commit agents 1020 identified by the ACM metadata1015. A primary commit agent 1020, in one embodiment, may be integratedwith the ACM 1011, the controller 1004, or the like. An ACM user 1016 orother third party, in certain embodiments, may provide a secondarycommit agent 1020 for ACM data that the ACM user 1016 or other thirdparty owns, and the primary commit agent 1020 may cooperate with theprovided secondary commit agent 1020 to process the ACM data. The one ormore commit agents 1020 for ACM data, in one embodiment, ensure and/orguarantee that the ACM data remains accessible to an owner of the ACMdata after a restart event. As described above with regard to triggeredcommit actions, a commit agent 1020 may process ACM metadata 1015 andassociated ACM data to perform one or more triggered commit actionsbefore, during, and/or after a trigger event, such as a failure or otherrestart event.

In one embodiment, a commit agent 1020, in cooperation with the ACM 1011or the like, may store the ACM metadata 1015 in a persistent ornon-volatile location in response to a restart or other trigger event.The commit agent 1020 may store the ACM metadata 1015 at a knownlocation, may store pointers to the ACM metadata 1015 at a knownlocation, may provide the ACM metadata 1015 to an external agent or datastore, or the like so that the commit agent 1020 may process the ACMmetadata 1015 and associated ACM data once the restart or other triggerevent has completed. The known location may include one or morepredefined logical block addresses or physical addresses of thenon-volatile memory 110, a predefined file, or the like. In certainembodiments, hardware of the ACM 1011 is configured to cooperate towrite the ACM metadata 1015 and/or pointers to the ACM metadata 1015 ata known location. In one embodiment, the known location may be atemporary location that stores the ACM data and ACM metadata 1015 untilthe host 1014 has recovered from a restart event and the commit agent1020 may continue to process the ACM data and ACM metadata 1015. Inanother embodiment, the location may be a persistent location associatedwith the ACM metadata 1015.

In response to completion of a restart event or other trigger event,during recovery, in one embodiment, a commit agent 1020 may locate andretrieve the ACM metadata 1015 from the non-volatile memory 110, from apredefined location or the like. The commit agent 1020, in response tolocating and retrieving the ACM metadata 1015, locates the ACM dataassociated with the retrieved ACM metadata 1015. The commit agent 1020,in certain embodiments, may locate the ACM data in a substantiallysimilar manner as the commit agent 1020 locates the ACM metadata 1015,retrieving ACM data from a predefined location, retrieving pointers tothe ACM data from a predefined location, receiving the ACM data from anexternal agent or data store, or the like. In one embodiment, the ACMmetadata 1015 identifies the associated ACM data and the commit agent1020 uses the ACM metadata 1015 to locate and retrieve the associatedACM data. For example, the commit agent 1020 may use a predefinedmapping to associate ACM data with ACM metadata 1015 (e.g., the Nthpiece of ACM data may be associated with the Nth piece of ACM metadata1015 or the like), the ACM metadata 1015 may include a pointer or indexfor the associated ACM data, or another predefined relationship mayexist between committed ACM metadata 1015 and associated ACM data. Inanother embodiment, an external agent may indicate to the commit agent1020 where associated ACM data is located.

In response to locating and retrieving the ACM metadata 1015 andassociated ACM data, the commit agent 1020 interprets the ACM metadata1015 and processes the associated ACM data based on the ACM metadata1015. For example, in one embodiment, the ACM metadata 1015 may identifya block storage volume and LBA(s) where the commit agent 1020 is towrite the ACM data upon recovery. In another embodiment, the ACMmetadata 1015 may identify an offset within a file within a file systemwhere the commit agent 1020 is to write the ACM data upon recovery. In afurther embodiment, the ACM metadata 1015 may identify an applicationspecific persistent object where the commit agent 1020 is to place theACM data upon recovery, such as a database record or the like. The ACMmetadata 1015, in an additional embodiment, may indicate a procedure forthe commit agent 1020 to call to process the ACM data, such as a delayedprocedure call or the like. In an embodiment where the ACM 1011advertises or presents volatile ACM buffers 1013 as non-volatile memory,the ACM metadata 1013 may identify an ACM buffer 1013 where the commitagent 1020 is to write the ACM data upon recovery.

In certain embodiments, the ACM metadata 1015 may identify one or moresecondary commit agents 1020 to further process the ACM metadata 1015and/or associated ACM data. A secondary commit agent 1020 may processACM metadata 1015 and associated ACM data in a substantially similarmanner to the commit agent 1020 described above. Each commit agent 1020may process ACM data in accordance with a different level or subset ofthe ACM metadata 1015, or the like. The ACM metadata 1015 may identify asecondary commit agent 1020, in various embodiments, by identifying aprogram/function of the secondary commit agent 1020 to invoke (e.g., afile path of the program), by including computer executable code of thesecondary commit agent 1020, by including a unique identifier indicatingwhich of a set of registered secondary commit agents 1020 to use, and/orby otherwise indicating a secondary commit agent 1020 associated withcommitted ACM metadata 1015.

In one embodiment, a secondary commit agent 1020 processes a remainingportion of the ACM metadata 1015 and/or of the ACM data after a previouscommit agent 1020 has processed the ACM metadata 1015 and/or the ACMdata. In a further embodiment, the ACM metadata 1015 may identifyanother non-volatile medium separate from the ACM 1011 for the secondarycommit agent 1020 to persist the ACM data even after a host experiencesa restart event. By committing the ACM metadata 1015 and the associatedACM data from the ACM buffers 1013 in response to a trigger event, suchas a failure or other restart condition, and processing the ACM metadata1015 and the associated ACM data once the trigger event has completed orrecovered, the ACM 1011 may guarantee persistence of the ACM data and/orperformance of the triggered commit action(s) defined by the ACMmetadata 1015.

The ACM 1011 is communicatively coupled to a host 1014, which, like thehost 114 described above, may comprise operating systems, virtualmachines, applications, a processor complex 1012, a central processingunit 1012 (CPU), and the like. In the FIG. 2 example, these entities arereferred to generally as ACM users 1016. Accordingly, as used herein, anACM user may refer to an operating system, a virtual machine operatingsystem (e.g., hypervisor), an application, a library, a CPUfetch-execute algorithm, or other program or process. The ACM 1011 maybe communicatively coupled to the host 1014 (as well as the ACM users1016) via a bus 1040, such as a system bus, a processor's memoryexchange bus, or the like (e.g., HyperTransport, QuickPath Interconnect(QPI), PCI bus, PCI-e bus, or the like). In some embodiments, the bus1040 comprises the primary power connection 1030 (e.g., the non-volatilestorage device 1102 may be powered through the bus 1040). Although someembodiments described herein comprise solid-state storage devices, suchas certain embodiments of the non-volatile storage device 1102, thedisclosure is not limited in this regard, and could be adapted to useany suitable recording/memory/storage device 1102 and/orrecording/memory/storage media 1110.

The ACM 1011 may be tightly coupled to the device used to perform thetriggered commit actions. For example, the ACM 1011 may be implementedon the same device, peripheral, card, or within the same “isolationzone” as the controller 1004 and/or secondary power source 1024. Thetight coupling of the ACM 1011 to the components used to implement thetriggered commit actions defines an “isolation zone,” which may providean acceptable level of assurance (based on industry standards or othermetric) that the ACM 1011 is capable of implementing the triggeredauto-commit actions in the event of a restart condition. In the FIG. 2example, the isolation zone of the ACM 1011 is provided by the tightcoupling of the ACM 1011 with the autonomous controller 1004 andsecondary power supply 1024 (discussed below).

The controller 1004 may comprise an I/O controller, such as a networkcontroller (e.g., a network interface controller), storage controller,dedicated restart condition controller, or the like. The controller 1004may comprise firmware, hardware, a combination of firmware and hardware,or the like. In the FIG. 2 example, the controller 1004 comprises astorage controller, such as the storage controller 104 and/ornon-volatile storage device controller described above. The controller1004 may be configured to operate independently of the host 1014. Assuch, the controller 1004 may be used to implement the triggered commitaction(s) of the ACM 1011 despite the restart conditions discussedabove, such as failures in the host 1014 (and/or ACM users 1016) and/orloss of the primary power connection 1030.

The ACM 1011 is powered by a primary power connection 1030, which, likethe primary power connection 130 described above, may be provided by asystem bus (bus 1040), external power supply, the host 1014, or thelike. In certain embodiments, the ACM 1011 also includes and/or iscoupled to a secondary power source 1024. The secondary power source1024 may power the ACM 1011 in the event of a failure to the primarypower connection 1030. The secondary power source 1024 may be capable ofproviding at least enough power to enable the ACM 1011 and/or controller1004 to autonomously implement at least a portion of a pre-configuredtriggered commit action(s) when the primary power connection 1030 hasfailed. The ACM 1011, in one embodiment, commits or persists at leastenough data (e.g., ACM data and ACM metadata 1015) while receiving powerfrom the secondary power source 1024, to allow access to the data oncethe primary power connection 1030 has been restored. In certainembodiments, as described above, the ACM 1011 may perform at least aportion of the pre-configured triggered commit action(s) after theprimary power connection 1030 has been restored, using one or morecommit agents 1020 or the like.

The ACM 1011 may comprise volatile memory storage. In the FIG. 2example, the ACM 1011 includes one or more auto-commit buffers 1013. Theauto-commit buffers 1013 may be implemented using a volatile RandomAccess Memory (RAM). In some embodiments, the auto-commit buffers 1013may be embodied as independent components of the ACM 1011 (e.g., inseparate RAM modules). Alternatively, the auto-commit buffers 1013 maybe implemented on embedded volatile memory (e.g., BRAM) available withinthe controller 1004, a processor complex 1012, an FPGA, or othercomponent of the ACM 1011.

Each of the auto-commit buffers 1013 may be pre-configured (armed) witha respective triggered commit action. In some embodiments, eachauto-commit buffer 1013 may comprise its own, respective ACM metadata1015. The ACM metadata 1015, in some embodiments, identifies how and/orwhere the data stored on the auto-commit buffer 1013 is to be committed.In some examples, the ACM metadata 1015 may comprise a logicalidentifier (e.g., an object identifier, logical block address (LBA),file name, or the like) associated with the data in the auto-commitbuffer 1013. The logical identifier may be predefined. In oneembodiment, when an auto-commit buffer 1013 is committed, the datatherein may be committed with the ACM metadata 1015 (e.g., the data maybe stored at a physical storage location corresponding to the logicalidentifier and/or in association with the logical identifier). Tofacilitate committing of ACM data during a hold-up time after a restartevent, the ACM 1011 may write ACM data and ACM metadata 1015 in a singleatomic operation, such as a single page write or the like. To permitwriting of ACM and ACM metadata 1015 in a single atomic operation, theACM buffers 1013 may be sized to correspond to a single write unit for anon-volatile storage media that is used by the ACM 1011. In someembodiments, the ACM metadata 1015 may comprise a network address, anLBA, or another identifier of a commit location for the data.

In a further embodiment, a logical identifier may associate data of anauto-commit buffer 1013 with an owner of the data, so that the data andthe owner maintain the ownership relationship after a restart event. Forexample, the logical identifier may identify an application, anapplication type, a process ID, an ACM user 1016, or another entity of ahost device 1014, so that the ACM data is persistently associated withthe identified entity. In one embodiment, a logical identifier may be amember of an existing namespace, such as a file system namespace, a usernamespace, a process namespace, or the like. In other embodiments, alogical identifier may be a member of a new or separate namespace, suchas an ACM namespace. For example, a globally unique identifiernamespace, as is typically used in distributed systems for identifyingcommunicating entities, may be used as an ACM namespace for logicalidentifiers. The ACM 1011 may process committed ACM data according to alogical identifier for the data once a restart event has completed. Forexample, the ACM 1011 may commit the ACM data to a logical identifierassociated with a temporary location in response to a restart event, andmay write the ACM data to a persistent location identified by anotherlogical identifier during recovery after the restart event.

As described above, the ACM 1011 may be tightly coupled with thecomponents used to implement the triggered commit actions (e.g., the ACM1011 is implemented within an “isolation zone”), which ensures that thedata on the ACM 1011 will be committed in the event of a restartcondition. As used herein, a “tight coupling” refers to a configurationwherein the components used to implement the triggered commit actions ofthe ACM 1011 are within the same “isolation zone,” or two or moredistinct trusted “isolation zones,” and are configured to operatedespite external failure or restart conditions, such as the loss ofpower, invalid shutdown, host 1014 failures, or the like. FIG. 2illustrates a tight coupling between the ACM 1011, the auto-commitbuffers 1013, the controller 1004, which is configured to operateindependently of the host 1014, and the secondary power source 1024,which is configured to power the controller 1004 and the ACM 1011(including the auto-commit buffers 1013) while the triggered commitactions are completed. Examples of a tight coupling include but are notlimited to including the controller 1004, the secondary power source1024, and the auto-commit buffers 1013 on a single printed circuit board(PCB), within a separate peripheral in electronic communication with thehost 1014, and the like. In other embodiments, the ACM 1011 may betightly coupled to other a different set of components (e.g., redundanthost devices, redundant communication buses, redundant controllers,alternative power supplies, and so on).

The ACM 1011 may be accessible by the host 1014 and/or ACM users 1016running thereon. Access to the ACM 1011 may be provided using memoryaccess semantics, such as CPU load/store commands, DMA commands, 3rdparty DMA commands, RDMA commands, atomic test and set commands,manipulatable memory pointers, and so on. In some embodiments, memorysemantic access to the ACM 1011 is implemented over the bus 1040 (e.g.,using a PCI-e BAR as described below).

In a memory semantic paradigm, ACM users 1016 running on the host 1014may access the ACM 1011 via a memory system 1018 of the host 1014. Thememory system 1018 may comprise a memory management unit, virtual memorysystem, virtual memory manager, virtual memory subsystem (or similarmemory address space) implemented by an operating system, avirtualization system (e.g., hypervisor), an application, or the like. Aportion of the ACM 1011 (e.g., one or more auto-commit buffers 1013) maybe mapped into the memory system 1018, such that memory semanticoperations implemented within the mapped memory address range (ACMaddress range 1021) are performed on the ACM 1011.

The storage management module 1050, in certain embodiments, allocatesand/or arbitrates the storage capacity of the ACM 1011 between multipleACM users 1016, using a resource management agent or the like. Theresource management agent of the storage management module 1050 maycomprise a kernel module provided to an operating system of the hostdevice 1014, a device driver, a thread, a user space application, or thelike. In one embodiment, the resource management agent determines howmuch storage capacity of the ACM buffers 1013 to allocate to an ACM user1016 and how long the allocation is to last. Because, in certainembodiments, the ACM 1011 commits or persists data across restartevents, the resource management agent may allocate storage capacity ofACM buffers 1013 across restart events.

The resource management agent may assign different ACM buffers 1013 todifferent ACM users 1016, such as different kernel and/or user spaceapplications. The resource management agent may allocate ACM buffers1013 to different usage types, may map ACM buffers 1013 to differentnon-volatile memory 110 locations for destaging, or the like. In oneembodiment, the resource management agent may allocate the ACM buffers1013 based on commit agents 1020 associated with the ACM buffers 1013 bythe ACM metadata 1015 or the like. For example, a master commit agent1020 may maintain an allocation map in ACM metadata 1015 identifyingallocation information for ACM buffers 1013 of the ACM 1011 andidentifying, in one embodiment, one or more secondary commit agents1020, and the master commit agent 1020 may allocate a portion of the ACMbuffers 1013 to each of the secondary commit agents 1020. In anotherembodiment, commit agents 1020 may register with the resource managementagent, may request resources such as ACM buffers 1013 from the resourcemanagement agent, or the like. The resource management agent may use apredefined memory management policy, such as a memory pressure policy orthe like, to allocate and arbitrate ACM buffer 1013 storage capacitybetween ACM users 1016.

In some embodiments, establishing an association between an ACM addressrange 1021 within the memory system 1018 and the ACM 1011 may comprisepre-configuring (arming) the corresponding auto-commit buffer(s) 1013with a triggered commit action. As described above, thispre-configuration may comprise associating the auto-commit buffer 1013with a logical identifier or other metadata, which may be stored in theACM metadata 1015 of the buffer 1013. As described above, the ACM 1011may be configured to commit the buffer data to the specified logicalidentifier in the event of a restart condition, or to perform otherprocessing in accordance with the ACM metadata 1015.

Memory semantic access to the ACM 1011 may be implemented using anysuitable address and/or device association mechanism. In someembodiments, memory semantic access is implemented by mapping one ormore auto-commit buffers 1013 of the ACM 1011 into the memory system1018 of the host 1014. In some embodiments, this mapping may beimplemented using the bus 1040. For example, the bus 1040 may comprise aPCI-e (or similar) communication bus, and the mapping may compriseassociating a Base Address Register (BAR) of an auto-commit buffer 1013of the ACM 1011 on the bus 1040 with the ACM address range 1021 in thememory system 1018 (e.g., the host 1014 mapping a BAR into the memorysystem 1018).

The association may be implemented by an ACM user 1016 (e.g., by avirtual memory system of an operating system or the like), through anAPI of a storage layer, such as the storage management layer (SML) 1050.The storage management module 1050 may be configured to provide accessto the auto-commit memory 1011 to ACM users 1016. The storage managementlayer 1050 may comprise a driver, kernel-level application, user-levelapplication, library, or the like. One example of an SML is the VirtualStorage Layer® of Fusion-io, Inc. of Salt Lake City, Utah. The storagemanagement module 1050 may provide a SML API 1019 comprising, interalia, an API for mapping portions of the auto-commit memory 1011 intothe memory system 1018 of the host 1014, for unmapping portions of theauto-commit memory 1011 from the memory system 1018 of the host 1014,for flushing the ACM buffers 1013, for accessing and managing persistentdata structures using the persistent data structure module 1009, or thelike. The storage management module 1050 may be configured to maintainmetadata 1051, which may include a forward index 1053 comprisingassociations between logical identifiers of a logical address space andphysical storage locations on the auto-commit memory 1011 and/orpersistent storage media. In some embodiments, ACM 1011 may beassociated with one or more virtual ranges that map to different addressranges of a BAR (or other addressing mechanism). The virtual ranges maybe accessed (e.g., mapped) by different ACM users 1016. Mapping orexposing a PCI-e ACM BAR to the host memory 1018 may be enabled ondemand by way of a SML API 1019 call.

The SML API 1019 may comprise interfaces for mapping an auto-commitbuffer 1013 into the memory system 1018. In some embodiments, the SMLAPI 1019 may extend existing memory management interfaces, such asmalloc, calloc, or the like, to map auto-commit buffers 1013 into thevirtual memory range of ACM user applications 1016 (e.g., a malloc callthrough the SML API 1019 may map one or more auto-commit buffers 1013into the memory system 1018). Alternatively, or in addition, the SML API1019 may comprise one or more explicit auto-commit mapping functions,such as “ACM_alloc,” “ACM_free,” or the like. Mapping an auto-commitbuffer 1013 may further comprise configuring a memory system 1018 of thehost to ensure that memory operations are implemented directly on theauto-commit buffer 1013 (e.g., prevent caching memory operations withina mapped ACM address range 1021).

The association between the ACM address range 1021 within the hostmemory system 1018 and the ACM 1011 may be such that memory semanticoperations performed within a mapped ACM address range 1021 areimplemented directly on the ACM 1011 (without intervening system RAM, orother intermediate memory, in a typical write commit operation,additional layers of system calls, or the like). For example, a memorysemantic write operation implemented within the ACM address range 1021may cause data to be written to the ACM 1011 (on one or more of theauto-commit buffers 1013). Accordingly, in some embodiments, mapping theACM address range 1021 may comprise disabling caching of memoryoperations within the ACM address range 1021, such that memoryoperations are performed on an ACM 1011 and are not cached by the host(e.g., cached in a CPU cache, in host volatile memory, or the like).Disabling caching within the ACM address range 1021 may comprise settinga “non-cacheable” flag attribute associated with the ACM range 1021,when the ACM range 1021 is defined.

As discussed above, establishing an association between the host memorysystem 1018 and the ACM 1011 may comprise “arming” the ACM 1011 toimplement a pre-determined triggered commit action. The arming maycomprise providing the ACM 1011 with a logical identifier (e.g., alogical block address, a file name, a network address, a stripe ormirroring pattern, or the like). The ACM 1011 may use the logicalidentifier to arm the triggered commit action. For example, the ACM 1011may be triggered to commit data to a persistent storage medium using thelogical identifier (e.g., the data may be stored at a physical addresscorresponding to the logical identifier and/or the logical identifiermay be stored with the data in a log-based data structure). Arming theACM 1011 allows the host 1014 to view subsequent operations performedwithin the ACM address range 1021 (and on the ACM 1011) as being“instantly committed,” enabling memory semantic write granularity (e.g.,byte level operations) and speed with instant commit semantics.

Memory semantic writes such as a “store” operation for a CPU aretypically synchronous operations such that the CPU completes theoperation before handling a subsequent operation. Accordingly, memorysemantic write operations performed in the ACM memory range 1021 can beviewed as “instantly committed,” obviating the need for a corresponding“commit” operation in the write-commit operation, which maysignificantly increase the performance of ACM users 1016 affected bywrite-commit latency. The memory semantic operations performed withinthe ACM memory range 1021 may be synchronous. Accordingly, ACM 1011 maybe configured to prevent the memory semantic operations from blocking(e.g., waiting for an acknowledgement from other layers, such as the bus1040, or the like). Moreover, the association between ACM address range1021 and the ACM 1011 allow memory semantic operations to bypass systemcalls (e.g., separate write and commit commands and their correspondingsystem calls) that are typically included in write-commit operations.

Data transfer between the host 1014 and the ACM 1011 may be implementedusing any suitable data transfer mechanism including, but not limitedto: the host 1014 performing processor IO operations (PIO) with the ACM1011 via the bus 1040; the ACM 1011 (or other device) providing one ormore DMA engines or agents (data movers) to transfer data between thehost 1014 and the ACM 1011; the host 1014 performing processor cachewrite/flush operations; or the like.

As discussed above, an ACM may be configured to automatically perform apre-configured triggered commit action in response to detecting certainconditions (e.g., restart or failure conditions). In some embodiments,the triggered commit action may comprise committing data stored on theACM 1014 to a persistent storage media. Accordingly, in someembodiments, an ACM, such as the ACM 1011 described above, may becomprise persistent storage media. FIG. 3 is a block diagram of a system1100 depicting an embodiment of a persistent data structure module 1009and an ACM 1111 configured to implement triggered commit actions, whichmay include committing data structures to a persistent, solid-state,and/or non-volatile storage.

The ACM 1111 of the FIG. 3 example may be tightly coupled to thenon-volatile storage device 1102, which comprises a controller 1104. Thecontroller 1104 may comprise a write data pipeline 1106 and a read datapipeline 1108, which may operate as described above. The non-volatilestorage device 1102 may be capable of persisting data on a non-volatilememory 1110, such as solid-state storage media.

A commit management apparatus 1122 is used to commit data to thenon-volatile memory 1110 in response to a trigger event, such as loss ofprimary power connection, or other pre-determined trigger event.Accordingly, the commit management apparatus 1122 may comprise and/or beconfigured to perform the functions of the auto-commit memory 1011described above. The commit management apparatus 1122 may be furtherconfigured to commit data on the ACM 1111 (e.g., the contents of theauto-commit buffers 1013) to the non-volatile memory 1110 in response toa restart condition (or on request from the host 1014 and/or ACM users1016) and in accordance with the ACM metadata 1015. The commitmanagement apparatus 1122 is one embodiment of a commit agent 1020.

The data on the ACM 1111 may be committed to the persistent storage 1110in accordance with the ACM metadata 1015, such as a logical identifieror the like. The ACM 1111 may commit the data to a temporary locationfor further processing after a restart event, may commit the data to afinal intended location, or the like as, described above. If thenon-volatile memory 1110 is sequential storage device, committing thedata may comprise storing the logical identifier or other ACM metadata1015 with the contents of the auto-commit buffer 1013 (e.g., in a packetor container header). If the non-volatile memory 1110 comprises a harddisk having a 1:1 mapping between logical identifier and physicaladdress, the contents of the auto-commit buffer 1013 may be committed tothe storage location to which the logical identifier maps. Since thelogical identifier or other ACM metadata 1015 associated with the datais pre-configured (e.g., armed), the ACM 1111 implements the triggeredcommit action independently of the host 1014. The secondary power supply1024 supplies power to the volatile auto-commit buffers 1013 of the ACM1111 until the triggered commit actions are completed (and/or confirmedto be completed), or until the triggered commit actions are performed toa point at which the ACM 1111 may complete the triggered commit actionsduring recovery after a restart event.

In some embodiments, the ACM 1111 commits data in a way that maintainsan association between the data and its corresponding logical identifier(per the ACM metadata 1015). If the non-volatile memory 1110 comprises ahard disk, the data may be committed to a storage location correspondingto the logical identifier, which may be outside of the isolation zone1301 (e.g., using a logical identifier to physical address conversion).In other embodiments in which the non-volatile memory 1110 comprises asequential media, such as solid-state storage media, the data may bestored sequentially and/or in a log-based format as described in aboveand/or in U.S. Provisional Patent Application Publication No.61/373,271, entitled “APPARATUS, SYSTEM, AND METHOD FOR CACHING DATA,”and filed 12 Aug. 2010, which is hereby incorporated by reference in itsentirety. The sequential storage operation may comprise storing thecontents of an auto-commit buffer 1013 with a corresponding logicalidentifier (as indicated by the ACM metadata 1015). In one embodiment,the data of the auto-commit buffer 1013 and the corresponding logicalidentifier are stored together on the media according to a predeterminedpattern. In certain embodiments, the logical identifier is stored beforethe contents of the auto-commit buffer 1013. The logical identifier maybe included in a header of a packet comprising the data, or in anothersequential and/or log-based format. The association between the data andlogical identifier may allow a data index to be reconstructed asdescribed above.

As described above, the auto-commit buffers 1013 of the ACM 1011 may bemapped into the memory system 1018 of the host 1014, enabling the ACMusers 1016 of access these buffers 1013 using memory access semantics.In some embodiments, the mappings between logical identifiers andauto-commit buffers 1013 may leverage a virtual memory system of thehost 1014.

For example, an address range within the memory system 1018 may beassociated with a “memory mapped file.” As discussed above, a memorymapped file is a virtual memory abstraction in which a file, portion ofa file, or block device is mapped into the memory system 1018 addressspace for more efficient memory semantic operations on data of thenon-volatile storage device 1102. An auto-commit buffer 1013 may bemapped into the host memory system 1018 using a similar abstraction. TheACM memory range 1021 may, therefore, be represented by a memory mappedfile. The backing file must be stored on the non-volatile memory 1110within the isolation zone 1301 (See FIG. 5 below) or another networkattached non-volatile storage device 1102 also protected by an isolationzone 1301. The auto-commit buffers 1013 may correspond to only a portionof the file (the file itself may be very large, exceeding the capacityof the auto-commit buffers 1013 and/or the non-volatile memory 1110).When a portion of a file is mapped to an auto-commit buffer 1013, theACM user 1016 (or other entity) may identify a desired offset within thefile and the range of blocks in the file that will operate with ACMcharacteristics (e.g., have ACM semantics). This offset will have apredefined logical identifier and the logical identifier and range maybe used to trigger committing the auto-commit buffer(s) 1013 mappedwithin the file. Alternatively, a separate offset for a block (or rangeof blocks) into the file may serve as a trigger for committing theauto-commit buffer(s) 1013 mapped to the file. For example, anytime amemory operation (load, store, poke, etc.) is performed on data in theseparate offset or range of blocks may result in a trigger event thatcauses the auto-commit buffer(s) 1013 mapped to the file to becommitted.

The underlying logical identifier may change, however (e.g., due tochanges to other portions of the file, file size changes, etc.). When achange occurs, the storage management module 1050 (via the SML API 1019,an ACM user 1016, the persistent data structure module 1009, or otherentity) may update the ACM metadata 1015 of the correspondingauto-commit buffers 1013. In some embodiments, the storage managementmodule 1050 may be configured to query the host 1014 (operating system,hypervisor, or other application) for updates to the logical identifierof files associated with auto-commit buffers 1013. The queries may beinitiated by the SML API 1019 and/or may be provided as a hook (callbackmechanism) into the host 1014. When the ACM user 1016 no longer needsthe auto-commit buffer 1013, the storage management module 1050 mayde-allocate the buffer 1013 as described above. De-allocation mayfurther comprise informing the host 1014 that updates to the logicalidentifier are no longer needed.

In some embodiments, a file may be mapped across multiple storagedevices (e.g., the storage devices may be formed into a RAID group, maycomprise a virtual storage device, or the like). Associations betweenauto-commit buffers 1013 and the file may be updated to reflect the filemapping. This allows the auto-commit buffers 1013 to commit the data tothe proper storage device. The ACM metadata 1015 of the auto-commitbuffers 1013 may be updated in response to changes to the underlyingfile mapping and/or partitioning as described above. Alternatively, thefile may be “locked” to a particular mapping or partition while theauto-commit buffers 1013 are in use. For example, if aremapping/repartitioning of a file is required, the correspondingauto-commit buffers 1013 may commit data to the file, and then bere-associated with the file under the new mapping/partitioning scheme.The SML API 1019 may comprise interfaces and/or commands for using thestorage management module 1050 to lock a file, release a file, and/orupdate ACM metadata 1015 in accordance with changes to a file.

Committing the data to solid-state, non-volatile storage 1110 maycomprise the storage controller 1104 accessing data from the ACM 1111auto-commit buffers 1013, associating the data with the correspondinglogical identifier (e.g., labeling the data), and injecting the labeleddata into the write data pipeline 1106 as described above. In someembodiments, to ensure there is a page program command capable ofpersisting the ACM data, the storage controller 1104 maintains two ormore pending page programs during operation. The ACM data may becommitted to the non-volatile memory 1110 before writing the power lossidentifier (power-cut fill pattern) described above.

FIG. 4 depicts one embodiment of a system 1200 comprising a persistentdata structure module 1009 and a plurality of auto-commit memories 1011.In the FIG. 4 example, memory semantic accesses implemented by the host1014 may be stored on a plurality of ACMs, including 1011A and 1011B. Insome embodiments, host data may be mirrored between the ACMs 1011A and1011B. The mirroring may be implemented using a multi-cast bus 1040.Alternatively, or in addition, one of the ACMs (AM 1011A) may beconfigured to rebroadcast data to the ACM 1011B. The ACMs 1011A and1011B may be local to one another (e.g., on the same local bus).Alternatively, the ACMs 1011A and 1011B may located on differentsystems, and may be communicatively coupled via a bus that supportsremove data access, such as Infiniband, a remote PCI bus, RDMA, or thelike.

In some embodiments, the ACMs 1011A and 1011B may implement a stripingscheme (e.g., a RAID scheme). In this case, different portions of thehost data may be sent to different ACMs 1011A and/or 1011B. Driver levelsoftware, such as a volume manager implemented by the storage managementmodule 1050 and/or operating system 1018 may map host data to the properACM per the striping pattern.

In some configurations, the memory access semantics provided by the ACMsmay be adapted according to a particular storage striping pattern. Forexample, if host data is mirrored from the ACM 1011A to the ACM 1011B, amemory semantic write may not complete (and/or an acknowledgement maynot be returned) until the ACM 1011A verifies that the data was sent tothe ACM 1011B (under the “instant commit” semantic). Similar adaptationsmay be implemented when ACMs are used in a striping pattern (e.g., amemory semantic write may be not return and/or be acknowledged, untilthe striping pattern for a particular operation is complete). Forexample, in a copy on write operation, the ACM 1011A may store the dataof an auto-commit buffer, and then cause the data to be copied to theACM 1011B. The ACM 1011A may not return an acknowledgment for the writeoperation (or allow the data to be read) until the data is copied to theACM 1011B.

The use of mirrored ACM devices 1011A and 1011B may be used in ahigh-availability configuration. For example, the ACM devices 1011A and1011B may be implemented in separate host computing devices. Memorysemantic accesses to the devices 1011A and 1011B are mirrored betweenthe devices as described above (e.g., using PCI-e access). The devicesmay be configured to operate in high-availability mode, such that deviceproxying may not be required. Accordingly, trigger operations (as wellas other memory semantic accesses) may be mirrored across both devices1011A and 1011B, but the devices 1011A and 1011B may not have to waitfor a “acknowledge” from the other before proceeding, which removes theother device from the write-commit latency path.

FIG. 5 is a block diagram of a one embodiment 1300 of a commitmanagement apparatus 1122. The commit management apparatus 1122 may betightly coupled (e.g., within an isolation zone 1301) to the auto-commitmemory 1011, the non-volatile storage controller 1304, the non-volatilestorage media 1310, and/or the secondary power supply 1324, one or moreof which may be in communication with and/or may cooperate with thepersistent data structure module 1009 to provide persistent datastructures. The tight coupling may comprise implementing thesecomponents 132, 1011, 1304, 1310, and/or 1324 on the same die, the sameperipheral device, on the same card (e.g., the same PCB), within apre-defined isolation zone, or the like. The tight coupling may ensurethat the triggered commit actions of the ACM buffers 1013 are committedin the event of a restart condition.

The commit management apparatus 1122 includes a monitor module 1310,which may be configured to detect restart conditions, such as power lossor the like. The monitor module 1310 may be configured to sensetriggering events, such as restart conditions (e.g., shutdown, restart,power failures, communication failures, host or application failures,and so on) and, in response, to initiate the commit module 1320 toinitiate the commit loss mode of the apparatus 1122 (failure loss mode)and/or to trigger the operations of other modules, such as modules 1312,1314, 1316, 1317, and/or 1318. The commit module 1320 includes anidentification module 1312, terminate module 1314, corruption module1316, and completion module 1318, which may operate as described above.

The identification module 1312 may be further configured to identifytriggered commit actions to be performed for each ACM buffer 1013 of theACM 1011. As discussed above, the identification module 1312 mayprioritize operations based on relative importance, with acknowledgedoperations being given a higher priority than non-acknowledgedoperations. The contents of auto-commit buffers 1013 that are armed tobe committed may be assigned a high priority due to the “instant commit”semantics supported thereby. In some embodiments, the ACM triggeredcommit actions may be given a higher priority than the acknowledgedcontents of the write data pipeline 1306. Alternatively, the contents ofarmed auto-commit buffers 1013 may be assigned the “next-highest’priority. The priority assignment may be user configurable (via an API,control (IOCTL), or the like).

The termination module 1314 terminates non-essential operations to allow“essential” to continue as described above. The termination module 1314may be configured to hold up portions of the ACM 1011 that are “armed”to be committed (e.g., armed auto-commit buffers), and may terminatepower to non-armed (unused) portions of the auto-commit memory 1011. Thetermination module 1314 may be further configured to terminate power toportions of the ACM 1011 (individual auto-commit buffers 1013) as thecontents of those buffers are committed.

The corruption module 1316 identifies corrupt (or potentially corrupt)data in the write data pipeline 1306 as described above. The module 1316may be further configured to identify corrupt ACM data 1011 (data thatwas written to the ACM 1011 during a power disturbance or other restartcondition). The corruption module 1316 may be configured to preventcorrupt data on the ACM 1011 from being committed in a triggered commitaction.

An ACM module 1317 is configured to access armed auto-commit buffers inthe auto-commit memory 1011, identify the ACM metadata 1015 associatedtherewith (e.g., label the data with the corresponding logicalidentifier per the ACM metadata 1015), and inject the data (andmetadata) into the write data pipeline of the non-volatile storagecontroller 1304. In some embodiments, the logical identifier (or otherACM metadata 1015) of the auto-commit buffer 1013 may be stored in thebuffer 1013 itself. In this case, the contents of the auto-commit buffer1013 may be streamed directly into a sequential and/or log-based storagedevice without first identifying and/or labeling the data. The ACMmodule 1317 may inject data before or after data currently in the writedata pipeline 1306. In some embodiments, data committed from the ACM1011 is used to “fill out” the remainder of a write buffer of the writedata pipeline 1306 (after removing potentially corrupt data). If theremaining capacity of the write buffer is insufficient, the write bufferis written to the non-volatile storage 1310, and a next write buffer isfilled with the remaining ACM data.

As discussed above, in some embodiments, the non-volatile storagecontroller 1304 may maintain an armed write operation (logical pagewrite) to store the contents of the write data pipeline 1306 in theevent of power loss. When used with an ACM 1011, two (or more) armedwrite operations (logical page writes) may be maintained to ensure thecontents of both the write data pipeline 1306, and all the armed buffers1013 of the ACM 1011 can be committed in the event of a restartcondition. Because a logical page in a write buffer may be partiallyfilled when a trigger event occurs, the write buffer is sized to hold atleast one more logical page of data than the total of all the datastored in all ACM buffers 1013 of the ACM 1011 and the capacity of datain the write data pipeline that has been acknowledged as persisted. Inthis manner, there will be sufficient capacity in the write buffer tocomplete the persistence of the ACM 1011 in response to a trigger event.Accordingly, the auto-commit buffers 1013 may be sized according to theamount of data the ACM 1011 is capable of committing. Once thisthreshold is met, the storage management module 1050 may reject requeststo use ACM buffers 1013 until more become available.

The completion module 1318 is configured to flush the write datapipeline regardless of whether the certain buffers, packets, and/orpages are completely filled. The completion module 1318 is configured toperform the flush (and insert the related padding data) after data onthe ACM 1011 (if any) has been injected into the write data pipeline1306. The completion module 1318 may be further configured to injectcompletion indicator into the write data pipeline, which may be used toindicate that a restart condition occurred (e.g., a restart conditionfill pattern). This fill pattern may be included in the write datapipeline 1306 after injecting the triggered data from the ACM 1011.

As discussed above, the secondary power supply 1324 may be configured toprovide sufficient power to store the contents of the ACM 1011 as wellas data in the write data pipeline 1306. Storing this data may compriseone or more write operations (e.g., page program operations), in whichdata is persistently stored on the non-volatile storage media 1310. Inthe event a write operation fails, another write operation, on adifferent storage location, may be attempted. The attempts may continueuntil the data is successfully persisted on the non-volatile storagemedia 1310. The secondary power supply 1324 may be configured to providesufficient power for each of a plurality of such page program operationsto complete. Accordingly, the secondary power supply 1324 may beconfigured to provide sufficient power to complete double (or more) pageprogram write operations as required to store the data of the ACM 1011and/or write data pipeline 1306.

FIG. 6 is a block diagram 1500 depicting a host computing device 1014with a persistent data structure module 1009 accessing an ACM 1011 usingmemory access semantics, providing persistent data structures incooperation with a file system module 1558 and/or an storage managementmodule 1050 (e.g., the storage management module 1050 described above).The host computing device 1014 may comprise a processor complex/CPU1012, which may include, but is not limited to, one or more of a generalpurpose processor, an application-specific processor, a reconfigurableprocessor (FPGA), a processor core, a combination of processors, aprocessor cache, a processor cache hierarchy, or the like. In oneembodiment, the processor complex 1012 comprises a processor cache, andthe processor cache may include one or more of a write combine buffer,an L1 processor cache, an L2 processor cache, an L3 processor cache, aprocessor cache hierarchy, and other types of processor cache. One ormore ACM users 1016 (e.g., operating systems, applications, and so on)operate on the host 1014.

The host 1014 may be communicatively coupled to the ACM 1011 via a bus1040, which may comprise a PCI-e bus, or the like. Portions of the ACM1011 are made accessible to the host 1014 may mapping in auto-commitbuffers 1013 into the host 1014. In some embodiments, mapping comprisesassociating an address range within the host memory system 1018 with anauto-commit buffer 1013 of the ACM 1011. These associations may beenabled using the SML API 1019 and/or storage management module 1050available on the host 1014.

The storage management module 1050 may comprise libraries and/or provideinterfaces (e.g., SML API 1019) to implement the memory access semanticsdescribed above. The API 1019 may be used to access the ACM 1011 usingmemory access semantics via a memory semantic access module 1522. Othertypes of access, such as access to the non-volatile storage 1502, may beprovided via a block device interface 1520.

The storage management module 1050 may be configured to memory mapauto-commit buffers 1013 of the ACM 1011 into the memory system 1018(via the SML API 1019). The memory map may use a virtual memoryabstraction of the memory system 1018. For example, a memory map may beimplemented using a memory mapped file abstraction. In this example, theoperating system (or application) 1016 designates a file to be mappedinto the memory system 1018. The file is associated with a logicalidentifier (LID) 1025 (e.g., logical block address), which may bemaintained by a file system, an operating system 1016, or the like.

The memory mapped file may be associated with an auto-commit buffer 1013of the ACM 1013. The association may be implemented by the storagemanagement module 1050 using the bus 1040. The storage management module1050 associates the address range of the memory mapped file (in thememory system 1018) with a device address of an auto-commit buffer 1013on the ACM 1011. The association may comprise mapping a PCI-e BAR intothe memory system 1018. In the FIG. 6 example, the ACM address range1021 in the memory system 1018 is associated with the auto-commit buffer1013.

As discussed above, providing memory access semantics to the ACM 1011may comprise “arming” the ACM 1011 to commit data stored thereon in theevent of failure or other restart. The pre-configured arming ensuresthat, in the event of a restart, data stored on the ACM 1011 will becommitted to the proper logical identifier. The pre-configuration of thetrigger condition enables applications 1016 to access the auto-commitbuffer 1013 using “instant-commit” memory access semantics. The logicalidentifier used to arm the auto-commit buffer may be obtained from anoperating system, the memory system 1018 (e.g., virtual memory system),or the like.

The storage management module 1050 may be configured to arm theauto-commit buffers 1013 with a logical identifier (e.g., automatically,by callback, and/or via the SML API 1019). Each auto-commit buffer 1013may be armed to commit data to a different logical identifier (differentLBA, persistent identifier, or the like), which may allow the ACM 1011to provide memory semantic access to a number of different, concurrentACM users 1016. In some embodiments, arming an auto-commit buffer 1013comprises setting the ACM metadata 1015 with a logical identifier. Inthe FIG. 6 example, the ACM address range 1021 is associated with thelogical identifier 1025, and the ACM metadata 1015 of the associatedauto-commit buffer is armed with the corresponding logical identifier1025.

The storage management module 1050 may arm an auto-commit buffer usingan I/O control (IOCTL) command comprising the ACM address range 1021,the logical identifier 1025, and/or an indicator of which auto-commitbuffer 1013 is to be armed. The storage management module 1050 (throughthe SML API 1019) may provide an interface to disarm or “detach” theauto-commit buffer 1013. The disarm command may cause the contents ofthe auto-commit buffer 1013 to be committed as described above (e.g.,committed to the non-volatile storage device 1502). The detach mayfurther comprise “disarming” the auto-commit buffer 1013 (e.g., clearingthe ACM metadata 1015). The storage management module 1050 may beconfigured to track mappings between address ranges in the memory system1018 and auto-commit buffers 1013 so that a detach command is performedautomatically.

Alternatively, or in addition, the storage management module 1050 may beintegrated into the operating system (or virtual operating system, e.g.,hypervisor) of the host 1014. This may allow the auto-commit buffers1013 to be used by a virtual memory demand paging system. The operatingsystem may (through the SML API 1019 or other integration technique)map/arm auto-commit buffers for use by ACM users 1016. The operatingsystem may issue commit commands when requested by an ACM user 1016and/or its internal demand paging system. Accordingly, the operatingsystem may use the ACM 1011 as another, generally available virtualmemory resource.

Once an ACM user 1016 has mapped the ACM address range 1021 to anauto-commit buffer 1013 and has armed the buffer 1013, the ACM user 1016may access the resource using memory access semantics, and may considerthe memory accesses to be “logically” committed as soon as the memoryaccess has completed. The ACM user 1016 may view the memory semanticaccesses to the ACM address range 1021 to be “instantly committed”because the ACM 1011 is configured to commit the contents of theauto-commit buffer (to the logical identifier 1025) regardless ofexperiencing restart conditions. Accordingly, the ACM user 1016 may notbe required to perform separate write and commit commands (e.g., asingle memory semantic write is sufficient to implement a write-commit).Moreover, the mapping between the auto-commit buffer 1013 and the ACM1011 disclosed herein removes overhead due to function calls, systemcalls, and even a hypervisor (if the ACM user 1016 is running in avirtual machine) that typically introduce latency into the write-commitpath. The write-commit latency time of the ACM user 1016 may thereforebe reduced to the time required to access the ACM 1011 itself.

As described above, in certain embodiments, the host 1014 may map one ormore ACM buffers 1013 into an address range of a physical memory addressspace addressable by a CPU, a kernel, or the like of the host device1014, such as the memory system 1018, as directly attached physicalmemory, as MMIO addressable physical memory over a PCI-e bus, orotherwise mapped as one or more pages of physical memory. The host 1014may further map at least a portion of the physically mapped ACM buffers1013 into a virtual memory address space, accessible to user-spaceprocesses or the like as virtual memory. The host 1014 may map theentire capacity of the physically mapped ACM buffers 1013 into a virtualmemory address space, a portion of the physically mapped ACM buffers1013 into a virtual memory address space, or the like.

In a similar manner, the host 1014 may include a virtual machinehypervisor, host operating system, or the like that maps the physicallymapped ACM buffers 1013 into an address space for a virtual machine orguest operating system. The physically mapped ACM buffers 1013 mayappear to the virtual machine or guest operating system as physicallymapped memory pages, with the virtual machine hypervisor or hostoperating system spoofing physical memory using the ACM buffers 1013. Aresource management agent, as described above, may allocate/arbitratestorage capacity of the ACM buffers 1013 among multiple virtualmachines, guest operating systems, or the like.

Because, in certain embodiments, virtual machines, guest operatingsystems, or the like detect the physically mapped ACM buffers 1013 as ifthey were simply physically mapped memory, the virtual machines cansub-allocate/arbitrate the ACM buffers 1013 into one or more virtualaddress spaces for guest processes, or the like. This allows processeswithin guest operating systems, in one embodiment, to change ACM dataand/or ACM metadata 1015 directly, without making guest operating systemcalls, without making requests to the hypervisor or host operatingsystem, or the like.

In another embodiment, instead of spoofing physical memory for a virtualmachine and/or guest operating system, a virtual machine hypervisor, ahost operating system, or the like of the host device 1014 may usepara-virtualization techniques. For example, a virtual machine and/orguest operating system may be aware of the virtual machine hypervisor orhost operating system and may work directly with it toallocate/arbitrate the ACM buffers 1013, or the like. When the ACM 1011is used in a virtual machine environment, in which one or more ACM users1016 operate within a virtual machine maintained by a hypervisor, thehypervisor may be configured to provide ACM users 1016 operating withinthe virtual machine with access to the SML API 1019 and/or storagemanagement module 1050.

The hypervisor may access the SML API 1019 to associate logicalidentifiers with auto-commit buffers 1013 of the ACM 1011, as describedabove. The hypervisor may then provide one or more armed auto-commitbuffers 1013 to the ACM users 1016 (e.g., by mapping an ACM addressrange 1021 within the virtual machine memory system to the one or moreauto-commit buffers 1013). The ACM user 1016 may then access the ACM1011 using memory access semantics (e.g., efficient write-commitoperations), without incurring overheads due to, inter alia, hypervisorand other system calls. The hypervisor may be further configured tomaintain the ACM address range 1021 in association with the auto-commitbuffers 1013 until explicitly released by the ACM user 1016 (e.g., thekeep the mapping from changing during use). Para-virtualization andcooperation, in certain embodiments, may increase the efficiency of theACM 1011 in a virtual machine environment.

In some embodiments, the ACM user 1016 may be adapted to operate withthe “instant commit” memory access semantics provided by the ACM 1013.For example, since the armed auto-commit buffers 1013 are triggered tocommit in the event of a restart (without an explicit commit command),the order in which the ACM user 1016 performs memory access to the ACM1011 may become a consideration. The ACM user 1016 may employ memorybarriers, complier flags, and the like to ensure the proper ordering ofmemory access operations.

For example, read before write hazards may occur where an ACM user 1016attempts to read data through the block device interface 1520 that isstored on the ACM 1011 (via the memory semantic interface 1522). In someembodiments, the storage management module 1050 may maintain metadatatracking the associations between logical identifiers and/or addressranges in the memory system 1018 and auto-commit buffers 1013. When anACM user 1016 (or other entity) attempts to access a logical identifierthat is mapped to an auto-commit buffer 1013 (e.g., through the blockdevice interface 1520), the storage management module 1050 directs therequest to the ACM 1011 (via the memory semantic interface 1522),preventing a read before write hazard.

The storage management module 1050 may be configured to provide a“consistency” mechanism for obtaining a consistent state of the ACM 1011(e.g., a barrier, snapshot, or logical copy). The consistency mechanismmay be implemented using metadata maintained by the storage managementmodule 1050, which, as described above, may track the triggeredauto-commit buffers 1013 in the ACM 1011. A consistency mechanism maycomprise the storage management module 1050 committing the contents ofall triggered auto-commit buffers 1013, such that the state of thepersistent storage is maintained (e.g., store the contents of theauto-commit buffers 1013 on the non-volatile storage 1502, or otherpersistent storage).

As described above, ACM users 1016 may access the ACM 1011 using memoryaccess semantics, at RAM granularity, with the assurance that theoperations will be committed if necessary (in the event of restart,failure, power loss, or the like). This is enabled by, inter alia, amapping between the memory system 1018 of the host 1014 andcorresponding auto-commit buffers 1013; memory semantic operationsimplemented within an ACM memory range 1021 mapped to an auto-commitbuffer 1013 are implemented directly on the buffer 1013. As discussedabove, data transfer between the host 1041 and the ACM 1011 may beimplemented using any suitable data transfer mechanism including, butnot limited to: the host 1014 performing processor IO operations (PIO)with the ACM 1011 via the bus 1040 (e.g., MMIO, PMIO, and the like); theACM 1011 (or other device) providing one or more DMA engines or agents(data movers) to transfer data between the host 1014 and the ACM 1011;the host 1014 performing processor cache write/flush operations; or thelike. Transferring data on the bus 1040 may comprise issuing a bus“write” operation followed by a “read.” The subsequent “read” may berequired where the bus 1040 (e.g., PCI bus) does not provide an explicitwrite acknowledgement.

In some embodiments, an ACM user may wish to transfer data to the ACM1011 in bulk as opposed to a plurality of small transactions. Bulktransfers may be implemented using any suitable bulk transfer mechanism.The bulk transfer mechanism may be predicated on the features of the bus1040. For example, in embodiments comprising a PCI-e bus 1040, bulktransfer operations may be implemented using bulk register store CPUinstructions.

Similarly, certain data intended for the ACM 1011 may be cached inprocessor cache of the processor complex 1012. Data that is cached in aprocessor cache may be explicitly flushed to the ACM 1011 (to particularauto-commit buffers 1013) using a CPU cache flush instruction, or thelike, such as the serializing instruction described below.

The DMA engines described above may also be used to perform bulk datatransfers between an ACM user 1016 and the ACM 1011. In someembodiments, the ACM 1011 may implement one or more of the DMA engines,which may be allocated and/or accessed by ACM users 1016 using thestorage management module 1050 (through the SML API 1019). The DMAengines may comprise local DMA transfer engines for transferring data ona local, system bus as well as RDMA transfer engines for transferringdata using a network bus, network interface, or the like.

In some embodiments, the ACM 1011 may be used in caching applications.For example, the non-volatile storage device 1502 may be used as cachefor other backing store, such as a hard disk, network-attached storage,or the like (not shown). One or more of the ACM 1011 auto-commit buffers1013 may be used as a front-end to the non-volatile storage 1502 cache(a write-back cache) by configuring one or more of the auto-commitbuffers 1013 of the ACM 1011 to commit data to the appropriate logicalidentifiers in the non-volatile storage 1502. The triggered buffers 1013are accessible to ACM users 1016 as described above (e.g., by mappingthe buffers 1013 into the memory system 1018 of the host 1014). Arestart condition causes the contents of the buffers 1013 to becommitted to the non-volatile storage 1502 cache. When the restartcondition is cleared, the cached data in the non-volatile storage 1502(committed by the auto-commit buffers 1013 on the restart condition)will be viewed as “dirty” in the write cache and available for useand/or migration to the backing store. The use of the ACM 1011 as acache front-end may increase performance and/or reduce wear on the cachedevice.

In some embodiments, auto-commit buffers 1013 of the ACM 1011 may beleveraged as a memory write-back cache by an operating system, virtualmemory system, and/or one or more CPUs of the host 1014. Data cached inthe auto-commit buffers 1013 as part of a CPU write-back cache may bearmed to commit as a group. When committed, the auto-commit buffers 1013may commit both data and the associated cache tags. In some embodiments,the write-back cache auto-commit buffers 1013 may be armed with an ACMaddress (or armed with a predetermined write-back cache address). Whenthe data is restored, logical identifier information, such as LBA andthe like, may be determined from a log or other data.

In some embodiments, the storage management module 1050 may compriselibraries and/or publish APIs adapted to a particular set of ACM users1016. For example, the storage management module 1050 may provide orcooperate with the persistent data structure module 1009, which may beadapted for applications whose performance is tied to write-commitlatency, such as transaction logs (database, file system, and othertransaction logs), store and forward messaging systems, persistentobject caching, storage device metadata, and the like. The persistentdata structure module 1009 may provide an Instant Committed Log Libraryor the like for a persistent transaction log, or another interface for adifferent persistent data structure.

The persistent data structure module 1009 provides mechanisms formapping auto-commit buffers 1013 of the ACM 1011 into the memory system1018 of an ACM user 1016 as described above. ACM users 1016 (or thepersistent data structure module 1009 itself) may implement an efficient“supplier/consumer” paradigm for auto-commit buffer 1013 allocation,arming, and access. For example, a “supplier” thread or process (in theapplication space of the ACM users 1016) may be used to allocate and/orarm auto-commit buffers 1013 for the ACM user 1016 (e.g., mapauto-commit buffers 1013 to address ranges within the memory system 1018of the host 1014, arm the auto-commit buffers 1013 with a logicalidentifier, and so on). A “consumer” thread or process of the ACM user1016 may then accesses the pre-allocated auto-commit buffers 1013. Inthis approach, allocation and/or arming steps are taken out of thewrite-commit latency path of the consumer thread. The consumer thread ofthe ACM user 1016 may consider memory semantic accesses to the memoryrange mapped to the triggered auto-commit buffers (the ACM memory range1021) as being “instantly committed” as described above.

Performance of the consumer thread(s) of the ACM user 1016 may beenhanced by configuring the supplier threads of the persistent datastructure module 1009 (or ACM user 1016) to allocate and/or armauto-commit buffers 1013 in advance. When a next auto-commit buffer 1013is needed, the ACM user 1016 have access a pre-allocated/armed bufferfrom a pool maintained by the supplier. The supplier may also performcleanup and/or commit operations when needed. For example, if datawritten to an auto-commit buffer is to be committed to persistentstorage, a supplier thread (or another thread outside of thewrite-commit path) may cause the data to be committed (using the SML API1019). Committing the data may comprise re-allocating and/or re-armingthe auto-commit buffer 1013 for a consumer thread of the ACM user 1016as described above.

The “supplier/consumer” approach described above may be used toimplement a “rolling buffer.” An ACM user 1016 may implement anapplication that uses a pre-determined amount of “rolling” data. Forexample, an ACM user 1016 may implement a message queue that stores the“last 20 inbound messages” and/or the ACM user 1016 may managedirectives for a non-volatile storage device (e.g., persistent trimdirectives or the like). A supplier thread may allocate auto-commitbuffers 1013 having at least enough capacity to hold the “rolling data”needed by the ACM user 1016 (e.g., enough capacity to hold the last 20inbound messages). A consumer thread may access the buffers using memoryaccess semantics (load and store calls) as described above. The SML API1019 (or supplier thread of the ACM user 1016) may monitor the use ofthe auto-commit buffers 1013. When the consumer thread nears the end ofits auto-commit buffers 1013, the supplier thread may re-initialize the“head” of the buffers 1013, by causing the data to be committed (ifnecessary), mapping the data to another range within the memory system1018, and arming the auto-commit buffer 1013 with a correspondinglogical identifier. As the consumer continues to access the buffers1013, the consumer stores new data at a new location that “rolls over”to the auto-commit buffer 1013 that was re-initialized by the supplierthread, and continues to operate. In some cases, data written to therolling buffers described above may never be committed to persistentstorage (unless a restart condition or other triggering conditionoccurs). Moreover, if the capacity of the auto-commit buffers 1013 issufficient to hold the rolling data of the ACM user, the supplierthreads may not have to perform re-initialize/re-arming described above.Instead, the supplier threads may simply re-map auto-commit buffers 1013that comprise data that has “rolled over” (and/or discard the “rolledover” data therein).

In its simplest form, a rolling buffer may comprise two ACM buffers1013, and the storage management module 1050 may write to one ACM buffer1013 for an ACM user 1016 while destaging previously written data fromthe other ACM buffer 1013 to a storage location, such as thenon-volatile memory 1110 or the like. In response to filling one ACMbuffer 1013 and completing a destaging process of the other ACM buffer1013, the storage management module 1050 may transparently switch thetwo ACM buffers such that the ACM user 1016 writes to the other ACMbuffer 1013 during destaging of the one ACM buffer 1013, in a ping-pongfashion. The storage management module 1050 may implement a similarrolling process with more than two ACM buffers 1013. The persistent datastructure module 1009, in certain embodiments, includes and/or supportsone or more transaction log API functions. An ACM user 1016 may use thepersistent data structure module 1009, in these embodiments, to declareor initialize a transaction log data structure.

As a parameter to a transaction log API command to create a transactionlog data structure, in one embodiment, the persistent data structuremodule 1009 receives a storage location, such as a location in anamespace and/or address space of the non-volatile storage 1502 or thelike, to which the storage management module 1050 may commit, empty,and/or destage data of the transaction log from two or more ACM buffers1013 in a rolling or circular manner as described above. Once an ACMuser 1016 has initialized or declared a transaction log data structure,in one embodiment, the use of two or more ACM buffers 1013 to implementthe transaction log data structure is substantially transparent to theACM user 1016, with the performance and benefits of the ACM 1011. Theuse of two or more ACM buffers 1013, in certain embodiments, istransparent when the destage rate for the two or more ACM buffers 1013is greater than or equal to the rate at which the ACM user 1016 writesto the two or more ACM buffers 1013. The persistent data structuremodule 1009, in one embodiment, provides byte-level writes to atransaction log data structure using two or more ACM buffers 1013.

In another example, a supplier thread may maintain four (4) or more ACMbuffers 1013. A first ACM buffer 1013 may be armed and ready to acceptdata from the consumer, as described above. A second ACM buffer 1013 maybe actively accessed (e.g., filled) by a consumer thread, as describedabove. A third ACM buffer 1013 may be in a pre-arming process (e.g.,re-initializing, as described above), and a fourth ACM buffer 1013 maybe “emptying” or “destaging” (e.g., committing to persistent storage, asdescribed above).

In some embodiments, the persistent data structure module 1009 and/orrolling log mechanisms described above may be used to implement anIntent Log for Synchronous Writes for a file system (e.g., the ZFS filesystem). The log data (ZIL) may be fairly small (1 to 4 gigabytes) andis typically “write only.” Reads may only be performed for file systemrecovery. One or more auto-commit buffers 1013 may be used to store filesystem data using a rolling log and/or demand paging mechanism asdescribed above.

The persistent data structure module 1009 may be configured to operatein a high-availability mode as described above in conjunction with FIG.4. In a high-availability mode, the storage management module 1050and/or bus 1040 sends commands pertaining to memory semantic accesses totwo or more ACM 1011, each of which may implement the requestedoperations and/or be triggered to commit data in the event of a restartcondition.

In certain embodiments, the persistent data structure module 1009 mayprovide access to persistent data structures as files in a file system,such as the depicted file system module 1558. The file system module1558, in one embodiment, may comprise a file system of the host device1014, and may be provided by an operating system, a storage subsystem,or the like. In a further embodiment, the file system module 1558 maycomprise a direct file system (DFS) for the ACM 1011 and/or thenon-volatile memory medium 110, 1110, 1502, bypassing one or moreoperating system or storage subsystem layers or the like to provideefficient, streamlined access to persistent data structures directly.

For example, in one embodiment, the file system module 1558 may lay outfiles directly in a sparse logical address space provided by the storagemanagement module 1050, which the storage management module 1050, thefile system module 1558, the metadata module 1912 described below, orthe like may map directly to physical locations in the ACM buffers 1013and/or the non-volatile memory medium 110, 1110, 1502. The file systemmodule 1558, in a further embodiment, may use or cooperate with thestorage management module 1050 and/or the ACM 1011 to perform blockallocations, ACM buffer 1013 allocations, and/or atomic data updates,each for the persistent data structure module 1009 or other storageclients. The file system module 1558 may support one or more file systeminterfaces or APIs such as open, close, read, write, pread, pwrite,lseek, mmap, or other requests or commands. The file system module 1558may comprise a kernel module in kernel-space, a user module inuser-space, or a combination of modules in both kernel-space anduser-space. The file system module 1558, in certain embodiments, may beintegrated with the storage management module 1050, a storage controller104, 1004, 1104, or the like, or may be an independent module ofcomputer executable program code and/or logic hardware.

As described above, the auto-commit memory module 1011, an associatedcommit agent 1020, or the like may be configured to commit, copy,transfer, synchronize, destage, persist, or preserve data from thevolatile ACM buffers 1013 to the non-volatile memory medium 110, 1110,1502, in response to a trigger such as a commit event, a restart event,a synchronize or destage request, a change in state, a change incondition, a change in a factor, a change in an attribute, a region ofan auto-commit buffer 1013 becoming full, or the like based on ACMmetadata 1015. Committing data, in one embodiment, may comprise copyingor transferring the data from an ACM buffer 1013 to a location in thenon-volatile memory medium 110, 1110, 1502. In a further embodiment,data is considered committed as soon as an ACM buffer 1013 has beenarmed or configured with ACM metadata 1015 defining or indicating acommit action for the data, due to the auto-commit memory module 1011'sguarantee of persistence.

The persistent data structure module 1009, in one embodiment, may beconfigured to provide data for a persistent data structure (e.g., inputdata for a data structure from a client) to the auto-commit memorymodule 1011 for writing to one or more ACM buffers 1013 so that thepersistent data structure is committed and/or ensured to be persisted inthe non-volatile memory medium 110, 1110, 1502 of the non-volatilestorage device 102, 1102. The persistent data structure module 1009 mayuse one or more ACM primitive operations to manage persistent datastructures using the auto-commit memory module 1011. For example, invarious embodiments, the persistent data structure module 1009 may usean ACM populate operation to load data of a persistent data structureinto an ACM buffer 1013, may use an ACM destage operation to destage,copy, transfer, and/or move data of a persistent data structure from anACM buffer 1013 to the non-volatile memory medium 110, 1110, 1502, mayuse an ACM barrier or ACM checkpoint operation to ensure consistency ofdata of a persistent data structure stored in an ACM buffer 1013, or thelike. In a further embodiment, one or more ACM buffers 1013 may bemapped into virtual memory of the host device 1014 or the like, and thepersistent data structure module 1009 may write, store, or load datainto an ACM buffer 1013 using memory semantic operations, as describedabove.

As described above, the storage management module 1050 (e.g., storagemanagement module 1050) may be configured to store data in thenon-volatile memory medium 110, 1110, 1502 sequentially, in a sequentialor chronological log-based writing structure 2140 as described belowwith regard to FIG. 11. The storage management module 1050 (e.g.,storage management module 1050) may map logical addresses of data tophysical locations storing the data in the non-volatile memory medium110, 1110, 1502 using a logical-to-physical address mapping structure2000 as described below with regard to FIG. 11. Persistent datastructures of the persistent data structure module 1009, in certainembodiments, may be accessible as files of the file system module 1558using file names. Persistent data structures, files of the file systemmodule 1558, or the like may be associated with logical identifiers(e.g., LBAs) in a logical address space provided by the storagemanagement module 1050 (e.g., storage management module 1050), which maycomprise a sparse logical address space that is larger than a physicalstorage capacity of the non-volatile storage device 102, 1102. Thepersistent data structure module 1009, the file system module 1558, thestorage management module 1050 (e.g., storage management module 1050),and/or the metadata module 1912 described below with regard to FIG. 10Bmay track which portions of a persistent data structure, a file, or thelike are stored in the ACM buffers 1013 and which portions are stored inthe non-volatile memory medium 110, 1110, 1502, maintaining suchmappings in file system metadata for the file system module 1558 or thelike.

In this manner, in certain embodiments, the file system module 1558 mayprovide access to a plurality of files using filenames, offsets, or thelike and the files (e.g., persistent data structures or other files) maybe stored in the ACM buffers 1013, the non-volatile memory medium 110,1110, 1502, and/or in both the ACM buffers 1013 and the non-volatilememory medium 110, 1110, 1502. Such cooperation between the persistentdata structure module 1009, the file system module 1558, the storagemanagement module 1050, and/or the auto-commit memory module 1011 may behidden or masked from applications or other clients, who may receive theaccess speed of the volatile ACM buffers 1013, the persistence of thenon-volatile memory medium 110, 1110, 1502, and the convenience of filesystem access to persistent data structures without managing orawareness of the underlying complexities.

Because the file system module 1559, in certain embodiments, isconfigured to provide access to files physically located in the ACMbuffers 1013 and/or the non-volatile memory medium 110, 1110, 1502,persistent data structures that are associated with filenames andaccessible as files through the file system module 1558, in oneembodiment, may be accessed (e.g., written to and/or read from) usingthe block device interface 1520, the memory semantic interface 1522,and/or file system operations provided by the file system module 1558.In one embodiment, the file system module 1558 opens a file as an ACMcontainer, with each block of data mapped to a location either in theACM buffers 1013 or the non-volatile memory medium 110, 1110, 1502, andthe mapping is updated as new data of the file is written, as data ofthe file is destaged from an ACM buffer 1013 to the non-volatile memorymedium 110, 1110, 1502, or the like.

The ACM 1011 disclosed herein may be used to enable other types ofapplications, such as durable synchronization primitives. Asynchronization primitive may include, but is not limited to: asemaphore, mutex, atomic counter, test and set, or the like.

A synchronization primitive may be implemented on an auto-commit buffer1013. ACM users 1016 (or other entities) that wish to access thesynchronization primitive may map the auto-commit buffer 1013 into thememory system 1018. In some embodiments, each ACM user 1016 may map thesynchronization primitive auto-commit buffer 1013 into its own,respective address range in the memory system 1018. Since the differentaddress ranges are all mapped to the same auto-commit buffer 1013, allwill show the same state of the synchronization primitive. ACM users1016 on remote computing devices may map the synchronization primitiveauto-commit buffer 1013 into their memory system using an RDMA networkor other remote access mechanism (e.g., Infiniband, remote PCI, etc.).

In some embodiments, the storage management module 1050 may comprise aDurable Synchronization Primitive Library (DSL) 1554 to facilitate thecreation of and/or access to synchronization primitives on the ACM 1011.The DSL 1554 may be configured to facilitate one-to-many mappings asdescribed above (one auto-commit buffer 1030-to-many address ranges inthe memory system 1018).

The ACM users 1016 accessing the semaphore primitive may consider theiraccesses to be “durable,” since if a restart condition occurs while thesynchronization primitive is in use, the state of the synchronizationprimitive will be persisted as described above (the auto-commit buffer1013 of the synchronization primitive will be committed to thenon-volatile storage 1502, or other persistent storage).

As described above, the storage management module 1050 may be used tomap a file into the memory system 1018 (virtual address space) of thehost 1014. The file may be mapped in an “Instant Committed Memory” (ICM)mode. In this mode, all changes made to the memory mapped file areguaranteed to be reflected in the file, even if a restart conditionoccurs. This guarantee may be made by configuring the demand pagingsystem to use an auto-commit buffer 1013 of the ACM 1011 for all “dirty”pages of the ICM file. Accordingly, when a restart condition occurs, thedirty page will be committed to the file, and no data will be lost.

In some embodiments, the storage management module 1050 may comprise anICM Library (ICML) 1556 to implement these features. The ICML 1556 maybe integrated with an operating system and/or virtual memory system ofthe host 1014. When a page of an ICM memory mapped file is to becomedirty, the ICML 1556 prepares an auto-commit buffer 1013 to hold thedirty page. The auto-commit buffer 1013 is mapped into the memory system1018 of the host 1014, and is triggered to commit to a logicalidentifier associated with the memory mapped file. As described above,changes to the pages in the memory system 1018 are implemented on theauto-commit buffer 1013 (via the memory semantic access module 1522).

The ICML 1556 may be configured to commit the auto-commit buffers 1013of the memory mapped file when restart conditions occur and/or when thedemand paging system of the host 1014 needs to use the auto-commitbuffer 1013 for another purpose. The determination of whether to“detach” the auto-commit buffer 1013 from a dirty page may be made bythe demand paging system, by the storage management module 1050 (e.g.,using a least recently used (LRU) metric, or the like), or by some otherentity (e.g., an ACM user 1016). When the auto-commit buffer isdetached, the storage management module 1050 may cause its contents tobe committed. Alternatively, the contents of the auto-commit buffer 1013may be transferred to system RAM at which point the virtual memorymapping of the file may transition to use a RAM mapping mechanisms.

In some embodiments, the storage management module 1050 (or ICML 1556)may be configured to provide a mechanism to notify the operating system(virtual memory system or the like) that a page of a memory mapped fileis about to become dirty in advance of an ACM user 1016 writing thedata. This notification may allow the operating system to prepare anauto-commit buffer 1013 for the dirty page in advance, and preventstalling when the write actually occurs (while the auto-commit buffer ismapped and armed). The notification and preparation of the auto-commitbuffer 1013 may implemented in a separate thread (e.g., a supplierthread as described above).

The storage management module 1050 and/or ICML 1556 may provide an APIto notify the operating system that a particular page that is about tobe written has no useful contents and should be zero filled. Thisnotification may help the operating system to avoid unnecessary readoperations.

The mechanisms for memory mapping a file to the ACM 1011 may be used inlog-type applications, or for other persistent data structures providedby the persistent data structure module 1009. For example, thepersistent data structure module 1009 may be configured to memory map alog file to one or more auto-commit buffers 1013 as described above. Asupplier thread may provide notifications to the operating systemregarding which pages are about to become dirty and/or to identify pagesthat do not comprise valid data.

Alternatively, or in addition, the ICML 1556 may be implemented withoutintegration into an operating system of the host 1014. In theseembodiments, the ICML 1556 may be configured to monitor and/or trapsystem signals, such as mprotect, mmap, and manual segmentation faultsignals to emulate the demand paging operations typically performed byan operating system.

FIG. 7 is a flow diagram of one embodiment of a method 1600 forproviding an auto-commit memory. At step 1610 the method 1600 may startand be initialized. Step 1610 may comprise the method 1600 initiatingcommunication with an ACM over a bus (e.g., initiating communicationwith ACM 1011 via bus 1040).

At step 1620, an auto-commit buffer of the ACM may be mapped into thememory system of a computing device (e.g., the host 1014). The mappingmay comprise associating a BAR address of the auto-commit buffer with anaddress range in the memory system.

At step 1630, the auto-commit buffer may be armed with ACM metadataconfigured to cause the auto-commit buffer to be committed to aparticular persistent storage and/or at a particular location in thepersistent storage in the event of a restart condition. In someembodiments, the ACM metadata may comprise a logical identifier such asa LBA, object identifier, or the like. Step 1630 may comprise verifyingthat the ACM metadata is valid and/or can be used to commit the contentsof the auto-commit buffer.

At step 1640, an ACM user, such as an operating system, application, orthe like, may access the armed auto-commit buffer using memory accesssemantics. The ACM user may consider the accesses to be “instantlycommitted” due to the arming of step 1630. Accordingly, the ACM user mayimplement “instant committed” writes that omit a separate and/orexplicit commit command. Moreover, since the memory semantic accessesare directly mapped to the auto-commit buffer (via the mapping of step1620), the memory semantic accesses may bypass systems calls typicallyrequired in virtual memory systems.

At step 1650 the method 1600 ends until a next auto-commit buffer ismapped and/or armed.

FIG. 8 is a flow diagram of another embodiment of a method 1700 forproviding an auto-commit memory. At step 1710 the method 1700 starts andis initialized as described above.

At step 1720, an auto-commit buffer of an ACM is mapped into the memorysystem of a computing device (e.g., the host 1014), and is armed asdescribed above.

At step 1730, an ACM user accesses the auto-commit buffer using memoryaccess semantics (e.g., by implementing memory semantic operationswithin the memory range mapped to the auto-commit buffer at step 1720).

At step 1740, a restart condition is detected. As described above, therestart condition may be a system shutdown, a system restart, a loss ofpower, a loss of communication between the ACM and the host computingdevice, a software fault, or any other restart condition that precludescontinued operation of the ACM and/or the host computing device.

At step 1750, the ACM implements the armed triggered commit actions onthe auto-commit buffer. The triggered commit action may comprisecommitting the contents of the auto-commit buffer to persistent storage,such as a solid-state or other non-volatile storage or the like.

At step 1760, the method 1700 ends until a next auto-commit buffer ismapped and/or armed or a restart condition is detected.

FIG. 9 is a flow diagram of another embodiment for providing anauto-commit memory. At step 1810, the method 1800 starts and isinitialized as described above. At step 1820, a restart condition isdetected.

At step 1830, the method 1800 accesses armed auto-commit buffers on theACM (if any). Accessing the armed auto-commit buffer may comprise themethod 1800 determining whether an auto-commit buffer has been armed byinspecting the triggered ACM metadata thereof. If no triggered ACMmetadata exists, or the ACM metadata is invalid, the method 1800 maydetermine that the auto-commit buffer is not armed. If valid triggeredACM metadata does exist for a particular auto-commit buffer, the method1800 identifies the auto-commit buffer as an armed buffer and continuesto step 1840.

At step 1840, the triggered commit action for the armed auto-commitbuffers is performed. Performing the triggered commit action maycomprise persisting the contents of the auto-commit buffer to asequential and/or log-based storage media, such as a solid-state orother non-volatile storage media. Accordingly, the triggered commitaction may comprise accessing a logical identifier of the auto-commitbuffer, labeling the data with the logical identifier, and injecting thelabeled data into a write data pipeline. Alternatively, the triggeredcommit action may comprise storing the data on a persistent storagehaving a one-to-one mapping between logical identifier and physicalstorage address (e.g., a hard disk). The triggered commit action maycomprise storing the contents of the armed auto-commit buffer to thespecified physical address.

Performing the triggered commit action at step 1840 may comprise using asecondary power supply to power the ACM, solid-state storage medium,and/or other persistent, non-volatile storage medium, until thetriggered commit actions are completed.

In certain embodiments, instead of or in addition to using a volatilememory namespace, such as a physical memory namespace, a virtual memorynamespace, or the like and/or instead of or in addition to using astorage namespace, such as a file system namespace, a logical unitnumber (LUN) namespace, or the like, one or more commit agents 1020, asdescribed above, may implement an independent persistent memorynamespace for the ACM 1011. For example, a volatile memory namespace,which is typically accessed using an offset in physical and/or virtualmemory, is not persistent or available after a restart event such as areboot, failure event, or the like and a process that owned the data inphysical and/or virtual memory prior to the restart event typically nolonger exists after the restart event. Alternatively, a storagenamespace is typically accessed using a file name and an offset, a LUNID and an offset, or the like. While a storage namespace may beavailable after a restart event, a storage namespace may have too muchoverhead for use with the ACM 1011. For example, saving a state for eachexecuting process using a file system storage namespace may result in aseparate file for each executing process, which may not be an efficientuse of the ACM 1011.

The one or more commit agents 1020 and/or the controller 1004, incertain embodiments, provide ACM users 1016 with a new type ofpersistent memory namespace for the ACM 1011 that is persistent throughrestart events without the overhead of a storage namespace. One or moreprocesses, such as the ACM user 1016, in one embodiment, may access thepersistent memory namespace using a unique identifier, such as aglobally unique identifier (GUID), universal unique identifier (UUID),or the like so that data stored by a first process for an ACM user 1016prior to a restart event is accessible to a second process for the ACMuser 1016 after the restart event using a unique identifier, without theoverhead of a storage namespace, a file system, or the like.

The unique identifier, in one embodiment, may be assigned to an ACM user1016 by a commit agent 1020, the controller 1004, or the like. Inanother embodiment, an ACM user 1016 may determine its own uniqueidentifier. In certain embodiments, the persistent memory namespace issufficiently large and/or ACM users 1016 determine a unique identifierin a predefined, known manner (e.g., based on a sufficiently unique seedvalue, nonce, or the like) to reduce, limit, and/or eliminate collisionsbetween unique identifiers. In one embodiment, the ACM metadata 1015includes a persistent memory namespace unique identifier associated withan owner of an ACM buffer 1013, an owner of one or more pages of an ACMbuffer 1013, or the like.

In one embodiment, the one or more commit agents 1020 and/or thecontroller 1004 provide a persistent memory namespace API to ACM users1016, over which the ACM users 1016 may access the ACM 1011 using thepersistent memory namespace. In various embodiments, the one or morecommit agents 1020 and/or the controller 1004 may provide a persistentmemory namespace API function to transition, convert, map, and/or copydata from an existing namespace, such as a volatile memory namespace ora storage namespace, to a persistent memory namespace; a persistentmemory namespace API function to transition, convert, map, and/or copydata from a persistent memory namespace to an existing namespace, suchas a volatile memory namespace or a storage namespace; a persistentmemory namespace API function to assign a unique identifier such as aGUID, a UUID, or the like; a persistent memory namespace API function tolist or enumerate ACM buffers 1013 associated with a unique identifier;a persistent memory namespace API function to export or migrate dataassociated with a unique identifier so that an ACM user 1016 such as anapplication and/or process may take its ACM data to a different host1014, to a different ACM 1011, or the like; and/or other persistentmemory namespace API functions for the ACM 1011.

For example, an ACM user 1016, in one embodiment, may use a persistentmemory namespace API function to map one or more ACM buffers 1013 of apersistent memory namespace into virtual memory of an operating systemof the host 1014, or the like, and the mapping into the virtual memorymay end in response to a restart event while the ACM user 1016 maycontinue to access the one or more ACM buffers 1013 after the restartevent using the persistent memory namespace. In certain embodiments, thestorage management module 1050 may provide the persistent memorynamespace API in cooperation with the one or more commit agents 1020and/or the controller 1004.

The persistent memory namespace, in certain embodiments, is a flatnon-hierarchical namespace of ACM buffers 1013 (and/or associated ACMpages), indexed by the ACM metadata 1015. The one or more commit agents1020 and/or the controller 1004, in one embodiment, allow the ACMbuffers 1013 to be queried by ACM metadata 1015. In embodiments wherethe ACM metadata 1015 includes a unique identifier, in certainembodiments, an ACM user 1016 may query or search the ACM buffers 1013by unique identifier to locate ACM buffers 1013 (and/or stored data)associated with a unique identifier. In a further embodiment, the one ormore commit agents 1020 and/or the controller 1004 may provide one ormore generic metadata fields in the ACM metadata 1015 such that an ACMuser 1016 may define its own ACM metadata 1015 in the generic metadatafield, or the like. The one or more commit agents 1020 and/or thecontroller 1004, in one embodiment, may provide access control for theACM 1011, based on unique identifier, or the like.

In one embodiment, an ACM buffer 1013 may be a member of a persistentmemory namespace and one or more additional namespaces, such as avolatile namespace, a storage namespace or the like. In a furtherembodiment, the one or more commit agents 1020 and/or the controller1004 may provide multiple ACM users 1016 with simultaneous access to thesame ACM buffers 103. For example, multiple ACM users 1016 of the sametype and/or with the same unique identifier, multiple instances of asingle type of ACM user 1016, multiple processes of a single ACM user1016, or the like may share one or more ACM buffers 1013. Multiple ACMusers 1016 accessing the same ACM buffers 1013, in one embodiment, mayprovide their own access control for the shared ACM buffers 1013, suchas a locking control, turn-based control, moderator-based control, orthe like. In a further embodiment, using a unique identifier, a new ACMuser 1016, an updated ACM user 1016, or the like on the host 1014 mayaccess

In certain embodiments, the ACM 1011 may comprise a plurality ofindependent access channels, buses, and/or ports, and may be at leastdual ported (e.g., dual ported, triple ported, quadruple ported). Inembodiments where the ACM 1011 is at least dual ported, the ACM 1011 isaccessible over a plurality of independent buses 1040. For example, theACM 1011 may be accessible over redundant bus 1040 connections with asingle host 1014, may be accessible to a plurality of hosts 1014 overseparate buses 104 with the different hosts 1014, or the like. Inembodiments where the ACM 1011 is at least dual ported, if one nodeand/or access channel fails (e.g., a host 1014, a bus 1040), one or moreadditional nodes and/or access channels to the ACM 1011 remainfunctional, obviating the need for redundancy, replication, or the likebetween multiple hosts 1014.

In one embodiment, the ACM 1011 comprises a PCI-e attached dual portdevice, and the ACM 1011 may be connected to and in communication withtwo hosts 1014 over independent PCI-e buses 1040. For example, the ACM1011 may comprise a plurality of PCI-e edge connectors for connecting toa plurality of PCI-e slot connectors, or the like. In a furtherembodiment, the power connection 1030 may also be redundant, with onepower connection 1030 per bus 1040 or the like. At least one of theplurality of connections, in certain embodiments, may comprise a datanetwork connection such as a NIC or the like. For example, the ACM 1011may comprise one or more PCI-e connections and one or more data networkconnections.

In one embodiment, the controller 1004 may arbitrate between a pluralityof hosts 1014 to which the ACM 1011 is coupled, such that one host 1014may access the ACM buffers 1013 at a time. The controller 1004, inanother embodiment, may accept a reservation request from a host 1014and may provide the requesting host 1014 with access to the ACM buffers1013 in response to receiving the reservation request. The ACM 1011 maynatively support a reservation request as an atomic operation of the ACM1011. In other embodiments, the ACM 1011 may divide ACM buffers 1013between hosts 1014, may divide ACM buffers 1013 between hosts but sharebacking non-volatile memory 1110 between hosts, or may otherwise dividethe ACM buffers 1013, the non-volatile memory 1110, and/or associatedaddress spaces between hosts 1014.

In one embodiment, the controller 1004, the one or more commit agents1020, and/or other elements of the ACM 1011 may be dual-headed,split-brained, or the like, each head or brain being configured tocommunicate with a host 1014 and with each other to provide redundantfunctions for the ACM 1011. By being at least dual ported, in certainembodiments, the ACM 1011 may be redundantly accessible, without theoverhead of replication, duplication, or the like which would otherwisereduce I/O speeds of the ACM 1011, especially if such replication,duplication, were performed over a data network or the like.

FIG. 10A depicts one embodiment of a persistent data structure module1009. The persistent data structure module 1009, in certain embodiments,may be substantially similar to the various embodiments of thepersistent data structure module 1009 described above. In otherembodiments, the persistent data structure module 1009 may include, maybe integrated with, and/or may be in communication with the storagemanagement module 1050, the storage controller 1004, 1104, 1304, and/orthe commit agent 1020.

In general, the persistent data structure module 1009 servicespersistent data structure requests from an ACM user 1016 or other clientfor the ACM 1011, in cooperation with a file system such as the filesystem module 1558, or the like. As described above with regard to theACM users 1016, as used herein, a client may comprise one or more of anapplication, operating system (OS), virtual operating platform (e.g., anOS with a hypervisor), guest OS, database system, process, thread,entity, utility, user, or the like, that is configured to access or usethe persistent data structure module 1009 and/or the ACM 1011. In thedepicted embodiment, the persistent data structure module 1009 includesa request module 1902, an allocation module 1904, a write module 1906,and a destage module 1908.

The persistent data structure module 1009, in certain embodiments,provides an interface whereby an application or other client may accesspersistent data structures stored in the byte addressable ACM buffers1013 and/or the non-volatile memory medium 110, whether the ACM buffers1013 are natively volatile or non-volatile, regardless of the type ofmedia used for the ACM buffers 1013, regardless of whether the datastructures are stored in the ACM buffers 1013, the non-volatile memorymedium 110, or a combination of both the ACM buffers 1013 and thenon-volatile memory medium 110. As described above, the volatile memorymodules (e.g., the ACM buffers 1013) of the ACM 1011 may be byteaddressable, write-in-place, volatile memory modules or devices, whilethe non-volatile memory medium 110, 1110, 1502 may be block addressable,using the block device interface 1520 described above or the like.

Instead of or in addition to the above methods of accessing the ACM1011, such as using a memory map (e.g., mmap) interface, in certainembodiments, the persistent data structure module 1009 may use the ACM1011 to expose persistent data structures to applications or otherclients using an API, shared library, file system namespace or otherpersistent logical identifiers, or the like as described above. Thepersistent data structure module 1009, in certain embodiments, maybypass one or more operating system and/or kernel layers, which mayotherwise reduce performance of the ACM 1011, complicate access topersistent data structures, or the like, increasing access times,introducing delays, or the like. The persistent data structure module1009 may provide access to persistent data structures using an existingI/O interface or namespace, such as a standard read/write API, a filesystem namespace, a LUN namespace, or the like or may provide a custompersistent data structure interface.

As described above, in certain embodiments, the persistent datastructure module 1009 and/or the ACM 1011 enable clients such as the ACMusers 1016 to access persistent data structures using fast,byte-addressable, persistent memory, combining benefits of volatilememory and non-volatile storage for persisting data structures.Auto-commit logic inside the hardware of the storage device 102, such asthe auto-commit memory 1011 described above with regard to FIG. 1, incertain embodiments, provides power-cut protection for data structureswritten to the auto-commit buffers 1013 of the ACM 1011. The persistentdata structure module 1009 and/or its sub-modules, in variousembodiments, may at least partially be integrated with a device driverexecuting on the processor 1012 of the host computing device 1014 suchas the storage management module 1050, may at least partially beintegrated with a hardware controller 1004, 1104 of the ACM 1011 and/ornon-volatile storage device 1102, as microcode, firmware, logiccircuits, or the like, or may be divided between a device driver and ahardware controller 1004, 1104, or the like.

In one embodiment, the request module 1902 is configured to monitor,detect, intercept, or otherwise receive requests for persistent datastructures from applications or other clients, such as the ACM users1016 described above, another module, a host computing device 1014, orthe like. The request module 1902 may receive data requests over an API,a shared library, a communications bus, the SML interface 1019, oranother interface. As used herein, a data request may comprise a storagerequest, a memory request, a file request, a persistent data structurerequest, an auto-commit request, or the like to access a data structure,such as the open, write/append, synchronize, close, map, and allocationpersistent data structure requests described below.

The request module 1902 may receive data requests using an existing orstandard I/O interface, such as read and write requests over the blockdevice interface 1520, load and store commands over the memory semanticinterface 1522, file system requests from the file system module 1558, acustom persistent data structure interface, or the like. By using theauto-commit buffers 1013 to support persistent data structure requestsor commands, in certain embodiments, the request module 1902 may allowapplications or other clients to access the ACM 1011 for persistent datastructures transparently, with little or no knowledge of the underlyingtiers of ACM 1011, non-volatile memory medium 110, or the like. Forexample, an application or other client may send persistent datastructure requests to the request module 1902 with little or noknowledge of whether the persistent data structure module 1009 servicesor satisfies the request using the auto-commit buffers 1013 or thenon-volatile memory media 1110, while receiving the benefit of both. Therequest module 1902 may intercept or otherwise receive data requestsusing an existing or standard interface, using a filter driver,overloading an interface, using LD_PRELOAD, intercepting or trapping asegmentation fault, using an IOCTL command, using a custom persistentdata structure interface, or the like.

As described below with regard to the allocation module 1904, in certainembodiments, a persistent data structure may be associated with apersistent logical identifier. Accordingly, a persistent data structurerequest may include a persistent logical identifier of the associatedpersistent data structure. A logical identifier, in one embodiment, is amember of a namespace. As used herein, a namespace comprises a containeror range of logical or physical identifiers that index or identify data,data locations, data structures, or the like. As described above,examples of namespaces may include a file system namespace, a LUNnamespace, a logical address space, a storage namespace, a virtualmemory namespace, a persistent ACM namespace, a volatile memorynamespace, an object namespace, a network namespace, a global oruniversal namespace, a BAR namespace, or the like.

A logical identifier may indicate a namespace to which a data structurebelongs. In one embodiment, a logical identifier may comprise a filename or other file identifier and/or an offset from a file systemnamespace, a LUN ID and an offset from a LUN namespace, an LBA or LBArange from a storage namespace, one or more virtual memory addressesfrom a virtual memory namespace, an ACM address from a persistent ACMnamespace, a volatile memory address from a volatile memory namespace ofthe host device 1014, an object identifier, a network address, a GUID,UUID, or the like, a BAR address or address range from a BAR namespace,or another logical identifier. In a further embodiment, a logicalidentifier may comprise a label or a name for a namespace, such as adirectory, a file path, a device identifier, or the like. In anotherembodiment, a logical identifier may comprise a physical address orlocation for a data structure. As described above, certain namespaces,and therefore namespace identifiers, may be temporary or volatile, andmay not be available to an ACM user 1016 or other client after a restartevent. Other namespaces, and associated logical identifiers, may bepersistent, such as a file system namespace, a LUN namespace, apersistent ACM namespace, or the like, and data structures associatedwith the persistent namespace may be accessible to an ACM user 1016 orother client after a restart event using the persistent logicalidentifier.

The request module 1902, in one embodiment, may receive an open requestfrom a client to open or initialize a persistent data structure. In afurther embodiment, the request module 1902 may receive a write request(e.g., for a transaction log data structure, an append request) from aclient to write and/or append data to a persistent data structure, usingthe ACM buffers 1013 or the like. The request module 1902, in anotherembodiment, may receive a synchronize request, a destage request, or thelike to trigger copying, destaging, transferring, migrating, orsynchronization of a data structure from an ACM buffer 1013 to thenon-volatile memory medium 110. The request module 1902, in oneembodiment, may receive a close request from a client to close, lock,delete, clear, or otherwise finish a data structure. In a furtherembodiment, the request module 1902 may receive a map request to map aregion of ACM 1011 (e.g., one or more ACM buffers 1013, pages, cachelines, memory locations, ranges of memory locations, or the like) intovirtual memory of the client on the host device 1014. The request module1902, in another embodiment, may receive an allocation request toallocate one or more regions of the ACM 1011 for storing a datastructure, a portion of a data structure, or the like.

The request module 1902, in certain embodiments, may receive persistentdata structure requests in user-space. As used herein, kernel-space maycomprise an area of memory (e.g., volatile memory, virtual memory, mainmemory) of the host computing device 1014; a set of privileges,libraries, or functions; a level of execution; or the like reserved fora kernel, operating system, or other privileged or trusted processes orapplications. User-space, as used herein, may comprise an area of memory(e.g., volatile memory, virtual memory, main memory) of the hostcomputing device 1014; a set of privileges, libraries, or functions; alevel of execution; or the like available to untrusted, unprivilegedprocesses or applications.

Due to access control restrictions, privilege requirements, or the likefor kernel-space, providing a device driver, library, API, or the likefor the ACM 1011 in kernel-space may have greater delays than inuser-space. Further, use of a storage stack of a kernel or operatingsystem, in certain embodiments, may introduce additional delays. Anoperating system or kernel storage stack, as used herein, may compriseone or more layers of device drivers, translation layers, file systems,caches, and/or interfaces provided in kernel-space, for accessing a datastorage device. The persistent data structure module 1009, in certainembodiments, may provide direct access to persistent data structuresand/or to the ACM 1011 by bypassing and/or replacing one or more layersof an operating system or kernel storage stack, reading and writing datastructures directly between the ACM buffers 1013 and/or the non-volatilememory medium 110 and user-space or the like. In a further embodiment,the request module 1902 may receive persistent data structure requestsin user-space from user-space applications or other clients and inkernel-space from kernel-space applications or other clients.

In one embodiment, the allocation module 1904 is configured toinitialize or open a new persistent data structure (e.g., a persistenttransaction log). For example, the allocation module 1904 may initializeor open a persistent data structure in response to a request received bythe request module 1902, such as an open request or the like. Theallocation module 1904, in certain embodiments, may associate a logicalidentifier with an opened or initialized persistent data structure. Forexample, the allocation module 1904 may cooperate with the file systemmodule 1558 to assign a filename to a persistent data structure, maycooperate with the storage management module 1050 to assign a range oflogical identifiers such as LBAs to a persistent data structure, maycooperate with the auto-commit memory module 1011 to assign a persistentACM identifier to a persistent data structure, or the like. In certainembodiments, the request module 1902 may receive a logical identifier,such as a filename, a range of LBAs, a LUN ID, or the like for apersistent data structure as a parameter of an open request, or thelike. In a further embodiment, the allocation module 1904, the filesystem module 1558, the storage management module 1050, the auto-commitmemory module 1011, or the like may assign a next available logicalidentifier to a persistent data structure or may use anotherpredetermined or known method to assign a logical identifier.

The allocation module 1904, in one embodiment, may allocate a region ofmemory of the auto-commit memory module 1011 for storing a persistentdata structure. As used herein, a region of memory may comprise a memorypage, a memory buffer, a range of memory addresses, a memory element, amemory module, and/or another subset of one or more ACM buffers 1013available to the auto-commit memory module 1011. In one embodiment, theallocation module 1904 may allocate a region of memory of the ACMbuffers 1013 for each requested persistent data structure. In a furtherembodiment, the allocation module 1904 may cooperate with theauto-commit memory module 1011 to dynamically allocate available memoryof the ACM buffers 1013, allocating memory to persistent data structuresas they are accessed, based on a frequency of access, a most recentaccess, an access history, an input rate or write rate, or the like forthe different persistent data structures.

In one embodiment, the write module 1906 is configured to receive,retrieve, transfer, or otherwise process input data from a client forwriting, updating, or appending to a persistent data structure. Forexample, a write request or append request received by the requestmodule 1902 may include or reference data to be written or appended to apersistent data structure identified by the request, which the writemodule 1906 may use to write the data to the ACM buffers 1013. In oneembodiment, the write module 1906 may write data of write requests tothe ACM buffers 1013 itself. In another embodiment, the write module1906 may monitor one or more regions of the ACM buffers 1013 or mayreceive an alert/notification that a client has written data to the oneor more regions of the ACM buffers 1013, or the like.

Depending on the type of persistent data structure, different dataoperations may be acceptable or supported. For example, in certainembodiments, a persistent transaction log may be strictly append only,while entries in a persistent linked-list may be overwritten, or thelike. In one embodiment, a write request may indicate where in apersistent data structure the associated data is to be written (e.g., towhich node, field, row, column, entry, or the like). In otherembodiments, a location for data may be defined by a rule, definition,or schema for a type of persistent data structure, such as anappend-only persistent transaction log or the like. A write request,append request, or the like, in one embodiment, may include datastructure metadata to be written with the associated write data (e.g., atimestamp, a sequence number, a label, an identifier, a pointer, or thelike. In another embodiment, the write module 1906 may determine datastructure metadata to be written with associated write data based on astate of a persistent data structure, based on metadata for a persistentdata structure from the metadata module 1912, by incrementing a pointer,a sequence number, or an identifier for a persistent data structure, orthe like.

The write module 1906, in certain embodiments, may write data to a datastructure, store data in a data structure, append data to a datastructure, or the like by writing or storing the data into a region ofthe ACM buffers 1013, which may guarantee or ensure persistence of thedata should a failure condition or restart event occur. In certainembodiments, if a persistent data structure has not been allocated amemory region in the ACM buffers 1013 or the like, the write module 1906may write data of a persistent data structure to the non-volatile memorymedium 110, 1110, 1502. In other embodiments, the write module 1906 maycooperate with the allocation module 1904 and/or the auto-commit memorymodule 1011 to allocate a memory region of the ACM buffers 1013 to apersistent data structure in response to a write request, an appendrequest, or the like for the persistent data structure.

The write module 1906 may cooperate with the metadata module 1912, thefile system module 1558, the storage management module 1050, and/or theauto-commit memory module 1011 to update logical-to-physical mappings,file system metadata, or the like for one or more logical identifiers ofan updated persistent data structure, as described below with regard tothe metadata module 1912. For example, in response to an append requestfor a persistent transaction log, the write module 1906 and/or themetadata module 1912 may extend a file length associated with a file ofthe persistent transaction log by the file system module 1558, add anentry in a logical-to-physical mapping structure mapping a range of LBAsfor the updated data to a location in the ACM buffers 1013 storing thedata, increment a pointer identifying an append point of the persistenttransaction log, or the like.

To provide the fast write times of the ACM buffers 1013 to applicationsor other clients writing to persistent data structures, even withrelatively small amounts or capacities of ACM buffers 1013, in oneembodiment, the write module 1906 may cooperate with the destage module1908 described below to use memory regions of the ACM buffers 1013 as aring buffer, a ping-pong buffer, a rolling buffer, a sliding window, orthe like, alternating between different memory regions of the ACMbuffers 1013 for writing data of a persistent data structure, while thedestage module 1908 destages, copies, or transfers data from a memoryregion not being written to. In this manner, the write module 1906 mayreuse or overwrite a region of memory of the ACM buffers 1013 only afterthe destage module 1908 has already destaged, copied, transferred,committed, or otherwise persisted the previously written data, providingefficient use of the ACM buffers 1013 while still ensuring persistence.

In certain embodiments, the write module 1906 may receive data from aclient and/or may write data at a different rate than the destage module1908 destages, copies, or transfers data to the non-volatile memorymedia 110, 1110, 1502. As used herein, an input rate comprises a rate atwhich the write module 1906 receives and/or writes data for one or morepersistent data structures. A transfer rate, as used herein, comprises arate at which the destage module 1908 transfers, copies, cleans, moves,synchronizes, or otherwise destages data of one or more persistent datastructures to the non-volatile memory medium 110, 1110, 1502. The writemodule 1906, in one embodiment, may cooperate with the destage module1908 to limit the input rate for a persistent data structure based onthe transfer rate for the persistent data structure, so that the writemodule 1906 does not overrun a region of memory allocated to thepersistent data structure.

Because the input rate and the transfer rate may not be constant, incertain embodiments, the write module 1906 may limit the input rate sothat over a predefined period of time, the input rate for a persistentdata structure is at or below the transfer rate. The input rate,however, in certain embodiments, may exceed the transfer rate at a givenmoment in time, so long as the write module 1906 does not overrun aregion of memory allocated to a persistent data structure. For example,the write module 1906 may limit an input rate based on an instantaneoustransfer rate, a moving average of sampled transfer rates, an amount ofmemory remaining in an allocated memory region, or the like. The writemodule 1906, in various embodiments, may limit an input rate byblocking, delaying, throttling, governing, sleeping, or otherwiselimiting a client process writing the data, or the like.

In one embodiment, the destage module 1908 is configured to destage datafrom the ACM buffers 1013 to the non-volatile memory medium 110, 1110,1502, such as persistent data structure data that the write module 1906has written to the ACM buffers 1013 as described above. The destagemodule 1908, in certain embodiments, cleans or destages data of the ACMbuffers 1013 that the non-volatile memory medium 110, 1110, 1502 doesnot yet store, such as new data, updated data, or the like. A locationfor the data in the non-volatile memory medium 110, 1110, 1502, such asan LBA, a physical address, or the like, may be indicated by ACMmetadata 1015 or other triggered commit metadata as described above. Thedestage module 1908, in certain embodiments, copies, transfers,destages, moves, or writes data from the ACM buffers 1013 to thenon-volatile memory medium 110, 1110, 1502 itself, based on ACM metadata1015, a dirty data bitmap, persistent data structure metadata from themetadata module 1912, or the like.

In a further embodiment, the destage module 1908 may cause data to becopied, transferred, destaged, moved, or written from the ACM buffers1013 to the non-volatile memory medium 110, 1110, 1502, by triggeringthe auto-commit memory module 1011, a commit management apparatus 1122,a commit agent 1020, or the like to perform a commit action for the dataidentified or defined by ACM metadata 1015 for the data. For example, asdescribed above, the auto-commit buffers 1013 may be armed with ACMmetadata 1015 to perform a commit action for preserving or persistingstored data. The destage module 1908 may utilize this pre-arming fordestaging, committing, or transferring data from the auto-commit buffers1013 to the non-volatile memory medium 110, 1110, 1502. The destagemodule 1908, in certain embodiments, may comprise, be in cooperationwith, or be integrated with the auto-commit memory module 1011, a commitmanagement apparatus 1122, a commit agent 1020, or the like.

While the write module 1906, in certain embodiments, may operate as aforeground process, writing data or allowing data to be written to theACM buffers 1013 in the foreground, the destage module 1908, in certainembodiments, may operate as a background process. For example, in oneembodiment, the destage module 1908 may destage, copy, transfer, move,or synchronize data periodically, lazily, during system downtime, duringa period of low traffic, or the like. In one embodiment, the destagemodule 1908 may destage, copy, transfer, move, or synchronize data inresponse to a trigger. The trigger may be the same or substantiallysimilar to the trigger for a commit action described above with regardto the ACM metadata 1015. In a further embodiment, the write module 1906may trigger the destage module 1908 based on an input rate, therebycontrolling a transfer rate of the destage module 1908.

The destage module 1908, in another embodiment, may be triggered inresponse to an amount of data of a persistent data structure stored in aregion of the ACM buffers 1013 exceeding a predefined threshold. Forexample, if the ACM buffers 1013 are organized into 4 KB pages, thedestage module 1908 may be triggered in response to the write module1906 filling a 4 KB page to destage, copy, transfer, or move the datafrom the 4 KB page to the non-volatile memory medium 110, 1110, 1502. Inanother embodiment, the destage module 1908 may be triggered in responseto the write module 1906 writing an amount of data equal to a page sizeor other region size of the non-volatile memory medium 1906, based on anarchitecture of the non-volatile memory medium 1906 or the like. In afurther embodiment, the destage module 1908 may be triggeredperiodically, in response to an elapsed time period since a previoustrigger or the like. In one embodiment, the destage module 1908 may betriggered by a monitoring device or monitoring module associated withthe memory of the ACM buffers 1013, such as the write module 1906, theauto-commit memory module 1011, or another module. In a furtherembodiment, the destage module 1908 may be triggered by asynchronization request, a destage request, or the like that the requestmodule 1902 receives from a client. The destage module 1908, in furtherembodiments, may be triggered by another determined change in state,change in condition, factor, or attribute of memory of the one or moreACM buffers 1013.

The destage module 1908, in one embodiment, copies, transfers, moves, ordestages data of a persistent data structure from the ACM buffers 1013in a manner whereby the data is no longer stored in the ACM buffers1013. For example, the destage module 1908 may erase or delete the datafrom the ACM buffers 1013 in response to storing the data in thenon-volatile memory media 110, 1110, 1502. In another embodiment, thedestage module 1908 may copy the data from the ACM buffers 1013 in amanner whereby a copy of the data remains in the ACM buffers 1013. Forexample, the destage module 1908 may allow the write module 1906 tooverwrite the data in the ACM buffers 1013 once the destage module 1908has stored the data in the non-volatile memory media 110, 1110, 1502, ata later time, as capacity of the ACM buffers 1013 is needed.

In one embodiment, the destage module 1908 may copy, destage, transfer,or write data from a memory region of the ACM buffers 1013 to thenon-volatile memory medium 110, 1110, 1502 in a manner that preserves anassociation of the data with a logical identifier of the persistent datastructure. For example, the destage module 1908 may write a filename, arange of logical addresses, or another logical identifier to thenon-volatile memory medium 110, 1110, 1502 with the data, may update alogical-to-physical mapping structure with a new physical location forthe data, may provide a new physical location for the data to themetadata module 1912, may update file system metadata indicating thatthe data is stored in the non-volatile memory medium 110, 1110, 1502, orthe like. By ensuring that data remains associated with a persistentlogical identifier, in certain embodiments, the destage module 1908ensures that the persistent data structure remains accessible to aclient using the persistent logical identifier.

In certain embodiments, the destage module 1908 transfers or destages anentire range or region of data regardless of whether a portion of thedata may already be stored in the non-volatile memory medium 110, 1110,1502. In another embodiment, the destage module 1908 may transfer ordestage just dirty data, data that is not yet stored in the non-volatilememory medium 110, 1110, 1502, without transferring or destaging cleandata that the non-volatile memory medium 110, 1110, 1502 already stores.In certain embodiments, the destage module 1908 transfers, copies, ordestages data from one or more auto-commit buffers 1013 to anotherlocation, such as the non-volatile memory medium 110, 1110, 1502 or thelike, that may have a larger capacity, a slower response time, or thelike than the one or more auto-commit buffers 1013.

The destage module 1908 may determine, based on a synchronization ordestage request, based on ACM metadata 1015, or the like whether thedestination for data of a persistent data structure is within thenon-volatile storage device 1102, in the non-volatile memory medium 110,1110, 1502 or the like, and may transfer or destage the data internallywithin the non-volatile storage device 1102. For example, the destagemodule 1908 may determine whether a destination namespace or addressspace of the data of a synchronization or destage request is associatedwith the non-volatile storage device 1102, such as the non-volatilememory medium 110, 1110, 1502, based on a destination logical identifierfor the data of the synchronization or destage request, and transfer ordestage the data from the ACM buffers 1013 internally within thenon-volatile storage device 1102 if the destination namespace or addressspace is associated with the non-volatile storage device 1102 (e.g., thedata is being transferred, copied, or moved within the non-volatilestorage device 1102, to another location in the ACM 1011, 1111, to thenon-volatile memory media 110, 1110, 1502, or the like).

If the destination for data of a synchronization or destage request, acommit location indicated by ACM metadata 1015, or the like is notlocated in the non-volatile storage device 1102, the destage module 1908may transfer or destage the data from the ACM 1011, 1111 to a locationexternal to the non-volatile storage device 1102, using a PIO operation,a DMA operation, a 3^(rd) party DMA operation, an RDMA operation, ablock device interface, an operating system storage stack, or the like,transferring the data over a system communications bus 1040, using aprocessor 1012 of the host device 1014, or the like. In response totransferring or destaging data of a destage request from one or moreauto-commit buffers 1013 of the ACM 1011, 1111, the destage module 1908may delete, remove, trim, invalidate, erase, or otherwise clear the datafrom the ACM 1011 and reuse the storage capacity associated with thedata in the one or more auto-commit buffers 1013.

In one embodiment, prior to transferring or destaging data from the ACM1011, the destage module 1908 may ensure consistency of the data (e.g.,that data is flushed from a processor complex 1012 of the host device1014 to the one or more auto-commit buffers 1013). For example, thedestage module 1908 may issue a serializing instruction that flushesdata from the processor complex 1012 to the one or more auto-commitbuffers 1013, may place a destage identifier or other marker in theprocessor complex 1012 associated with the non-volatile storage device1102 (e.g., storing the destage identifier or other marker to a virtualmemory address mapped to a control status register or other predefinedlocation within the non-volatile storage device 1102), may issuing asecond serializing instruction to flush the destage identifier or othermarker from the processor complex 1012, or the like. The destage module1908 may transfer, destage, or otherwise write data from the ACM buffers1013 to a destination location in response to receiving a destageidentifier or other marker in the non-volatile storage device 1102,indicating successful completion of the first serializing instructionand consistency of the data to be destaged.

As described above with regard to the write module 1906, the destagemodule 1908 and the write module 1906 may cooperate to use two or moreregions of the ACM buffers 1013 as a ring buffer, a ping-pong buffer, arolling buffer, a sliding window, or the like, alternating betweendifferent memory regions of the ACM buffers 1013 for destaging data of apersistent data structure, while the write module 1906 writes data to amemory region from which the destage module 1908 is not currentlydestaging data, making efficient use of the ACM buffers 1013 while stillensuring persistence.

The destage module 1908 may cooperate with the write module 1906, asdescribed above, to ensure that a transfer rate for a persistent datastructure, for the ACM buffers 1013, or the like, at least on average orover time, matches or exceeds an input rate for the persistent datastructure, for the ACM buffers 1013, or the like. The write module 1906,in various embodiments, may limit an input rate as described above. Incertain embodiments, in addition to or instead of the write module 1906limiting an input rate, the destage module 1908 may increase thetransfer rate for a persistent data structure, in response to anincrease in the input rate for the persistent data structure, or thelike. The write module 1906 and/or the destage module 1908 may manage aninput rate and/or a transfer rate for an individual persistent datastructure, for a set of persistent data structures, for one or moreregions of the ACM buffers 1013, for the entire ACM 1011, or at anothergranularity.

In one embodiment, the destage module 1908 may increase a transfer rateby increasing a quantity or size of data copied, transferred, ordestaged from the ACM buffers 1013 to the non-volatile memory medium110, 1110, 1502 at a time, in a single transaction, or the like. Forexample, the destage module 1908 may initially copy, transfer, ordestage data a page at a time, and may increase a quantity or size ofdata to two pages, three pages, four pages, or the like over time inresponse to an increasing input rate. In a further embodiment, thedestage module 1908 may increase a transfer rate by increasing a numberof parallel destage processes or threads executing at a time to copy,transfer, or destage data. In certain embodiments, the destage module1908 may increase both a transfer size and a number of parallel destageprocesses or threads to increase a transfer rate.

The manner in which the destage module 1908 increases a transfer rate,in certain embodiments, may depend on a magnitude of the input rate thatthe destage module 1908 is trying to track or match. For example,increasing a size quantity of data copied to the non-volatile memorymedium 110, 1110, 1502 per transfer operation may be more effective forthe destage module 1908 below a threshold input rate, transfer rate, ordestage size but increasing a number of parallel transfer processescopying data may be more effective for the destage module 1908 above thethreshold input rate, transfer rate, or destage size.

In certain embodiments, the destage module 1908 and/or the write module1906 may manage an input rate and/or a transfer rate so that at least apredefined amount of extra or spare memory capacity remains for apersistent data structure, acting as padding or a buffer between thewrite module 1906 and the destage module 1908. For example, the writemodule 1906 and/or the destage module 1908 may manage an input rate anda transfer rate so that about one third of the allocated memory capacityremains as padding or a buffer, while about one third of the allocatedmemory capacity is used by the write module 1906 and one third of theallocated memory capacity is used by the destage module 1908, or thelike. Depending on the architecture and transfer speeds of the ACMbuffers 1013, of the non-volatile memory medium 110, 1110, 1502, or thelike, other ratios may be more or less optimal and the write module 1906and/or the destage module 1908 may manage the input rate and/or thetransfer rate accordingly.

In certain embodiments, instead of managing the input rate and/ortransfer rate for a persistent data structure, the destage module 1908may allow the persistent data structure to become out of synchronizationor transactionally inconsistent, until an owner or other client issues asynchronization request to the request module 1902. In such embodiments,the destage module 1908 may further destage, copy, or transfer data tomanage an available storage capacity for the ACM buffers 1013, even ifan owner or client of a persistent data structure has not sent asynchronization request. In this manner, in certain embodiments, anapplication or other client can write data to a persistent datastructure as fast as they desire, up to architectural or physicalconstraints of the ACM buffers 1013, without the write module 1906limiting the input rate, and may simply issue a synchronization requestto the request module 1902 to synchronize or checkpoint the persistentdata structure as desired.

FIG. 10B depicts another embodiment of a persistent data structuremodule 1009. In one embodiment, the persistent data structure module1009 may be substantially similar to one or more of the persistent datastructure modules 1009 described above. In the depicted embodiment, thepersistent data structure module 1009 of FIG. 10B includes a requestmodule 1902, a write module 1906, a destage module 1908 and furtherincludes an enforcement module 1910, a metadata module 1912, a readmodule 1914, a close module 1916, and a map module 1918.

In one embodiment, the enforcement module 1910 is configured to enforceone or more rules for a persistent data structure and/or a persistentdata structure type. For example, each different type of data structuremay be defined or structured by a set of one or more rules,restrictions, definitions, or the like. The rules may define one or moreallowed or acceptable data operations for a data structure. For atransaction log, the enforcement module 1910 may enforce one or morerules such as that entries must be sequential, that data entries may notbe overwritten or updated once written, or the like. The enforcementmodule 1910 may enforce different rules for different types of datastructures. For example, the enforcement module 1910 may enforce astrict FIFO rule for a persistent queue data structure, may enforce astrict LIFO rule for a persistent stack data structure, may enforce astrict order or hierarchy for data entries or nodes for a persistenttree data structure, may enforce a rule requiring certain data types orrequired fields or entries for a certain persistent data structure, orthe like.

The enforcement module 1910, in one embodiment, cooperates with therequest module 1902 to provide an interface, such as an API, a sharedlibrary, a communications protocol, or the like that enforces orrequires satisfaction of one or more rules for a persistent datastructure. For example, the enforcement module 1910 and the requestmodule 1902, instead of supporting a write request with parameters for alogical identifier and an offset to which data is to be written relativeto the logical identifier, may support an append request for apersistent transaction log with a logical identifier parameter butwithout an offset or address parameter, so that the write module 1906appends the data to the identified persistent transaction log, and nooffset or address within the persistent transaction log may bespecified, enforcing the rules of the persistent transaction log. Inthis manner, the enforcement module 1910 may enforce one or more rulesfor a persistent data structure passively, by way of an interface.

In certain embodiments, the enforcement module 1910 may enforce one ormore rules for a persistent data structure by actively blocking,intercepting, or stopping execution of requests or operations thatviolate the one or more rules. For example, the enforcement module 1910may actively monitor a region of memory allocated to a persistenttransaction log, and may actively block or otherwise prevent writes toanywhere but a location of an append point, so that data may not beoverwritten. In one embodiment, the enforcement module 1910 may enforceone or more rules or definitions for a persistent data structure using acombination of both passive interface definitions and active blocking.For example, the enforcement module 1910 may cooperate with the requestmodule 1902 to provide an append-only interface for a persistenttransaction log, and may actively block or prevent overwriting data ofthe persistent transaction log using a different interface, such as theblock device interface 1520, the memory semantic interface 1522, or thelike. In this manner, the enforcement module 1910 may prevent anapplication or other client from inadvertently or accidently overwritingor otherwise violating the integrity of a persistent data structure,ensuring that the persistent data structure satisfies the datastructure's strict definition, rules, or the like.

In one embodiment, the metadata module 1912 maintains and/or providesaccess to metadata tracking which data of one or more persistent datastructures is stored in or resides in volatile memory of the ACM buffers1013 and which data is stored in or resides in the non-volatile memorymedium 110, 1110, 1502. For example, the metadata module 1912 maymaintain a clean/dirty bitmap, table, or other data structure indicatingwhich data is stored in the ACM buffers 1013 but not yet stored by thenon-volatile memory medium 110, 1110, 1502, using flags or otherindicators representing a state of the associated data. In a furtherembodiment, the metadata module 1912 may track which data is stored inthe ACM buffers 1013 and which data is stored in the non-volatile memorymedium 110, 1110, 1502 using one or more logical-to-physical mappingstructures, mapping logical identifiers for persistent data structuresto physical locations in either the ACM buffers 1013 or the non-volatilememory medium 110, 1110, 1502. For example, the metadata module 1912 maycooperate with the file system module 1558 to maintain file systemmetadata tracking or mapping file names and offsets to locations in oneor more of the ACM buffers 1013 and the non-volatile memory medium 110,1110, 1502, may cooperate with the storage management module 1050 tomaintain a logical-to-physical mapping structure tracking or mappinglogical addresses such as LBAs to physical locations in one or more ofthe ACM buffers 1013 and the non-volatile memory medium 110, 1110, 1502,or the like.

The metadata module 1912 may update the metadata in response to thewrite module 1906, a client, or the like writing data to the ACM buffers1013, in response to the destage module 1908 destaging, cleaning,copying, writing, or otherwise storing data from the ACM buffers 1013 tothe non-volatile memory medium 110, 1110, 1502, or the like. Themetadata module 1912, in certain embodiments, may scan or process datain the non-volatile memory medium 110, 1110, 1502 during recovery from arestart event, a failure condition, or the like to reconstruct lostmetadata, repair damaged metadata, or the like, so thatlogical-to-physical mappings are accurate and so that the request module1902, the write module 1906, the read module 1914, the file systemmodule 1558, and/or the storage management module 1050, may provideaccess to persistent data structures after the restart event, using datathe ACM 1011 committed or flushed to the non-volatile memory medium 110,1110, 1502 in response to detecting the restart event, the failurecondition, or another trigger.

The allocation module 1904, the write module 1906, the destage module1908, the read module 1914, the close module 1916, the map module 1918,the file system module 1558, and/or the storage management module 1050may be configured to satisfy or fulfil one or more requests for apersistent data structure, even if the persistent data structureincludes data stored both in volatile memory of the ACM buffers 1013 andin the non-volatile memory medium 110, 1110, 1502, based on metadatafrom the metadata module 1912 indicating one or more locations for thepersistent data structure based on a logical identifier associated withthe data.

In one embodiment, the read module 1914 provides data of a persistentdata structure to a requesting client. The read module 1914 may copy orload a persistent data structure or a requested portion of thepersistent data structure into an ACM buffer 1013 mapped into virtualmemory of a client on the host device 1014, directly into volatilememory of the host device 1014 itself, may provide a persistent datastructure or portion thereof over the block device interface 1520, thememory semantic interface 1522, the SML API 1019, a persistent datastructure interface, or the like. The read module 1914, in certainembodiments, may provide access to a persistent data structure residingin both volatile memory of the ACM buffers 1013 and in the non-volatilememory medium 110, 1110, 1502 by looking up a logical identifier for thepersistent data structure in metadata from the metadata module 1912, andretrieving the different portions of the persistent data structure toprovide to a requesting client.

In one embodiment, the close module 1916 is configured to close apersistent data structure in response to the request module 1902receiving a close request for the persistent data structure from aclient. Closing a persistent data structure, in one embodiment,comprises locking the persistent data structure, rendering it read-only.In another embodiment, the close module 1916 may close a persistent datastructure by invalidating, deleting, erasing, trimming, removing, orotherwise clearing the data of a persistent data structure from the ACMbuffers 1013 and/or the non-volatile memory medium 110, 1110, 1502. Theclose module 1916 may check metadata maintained by the metadata module1912, using a logical identifier from a close request for a persistentdata structure, to determine locations for the persistent data structurebeing closed in the ACM buffers 1013 and/or the non-volatile memorymedium 110, 1110, 1502. In embodiments where the close module 1916invalidates or marks data of a closed persistent data structure fordeletion, a separate garbage collection or storage capacity recoveryprocess may reclaim storage capacity of the closed persistent datastructure at a later time.

In one embodiment, the map module 1918 is configured to map one or moreregions of the ACM buffers 1013 into virtual memory of a client on thehost device 1014, in response to the request module 1902 receiving a maprequest from the client. In certain embodiments, the map module 1918 maymap a region of the ACM buffers 1013 associated with a persistent datastructure into virtual memory to provide access to the persistent datastructure. In certain embodiments, the map module 1918 may map a file ofa persistent data structure into virtual memory, in cooperation with thefile system module 1558 or the like, using memory mapped file I/O inresponse to a map request from a client with a file name or otherlogical identifier for the persistent data structure. A variety ofmemory mapping technologies, such as MMIO, port I/O, PMIO, memory mappedfile I/O, and the like are described above whereby the ACM 1011 may beaccessed. The map module 1918 may use one or more of these or othermemory mapping technologies to provide memory semantic access to apersistent data structure.

As described above, once data has been stored in the auto-commit buffers1013, the ACM 1011 preserves or persists the data in non-volatile memorymedia 110, 1110, 1110, 1502 and provides the data from the non-volatilememory media 110, 1110, 1502 to clients, such as ACM users 1016, afterrecovery from the restart event. The persistent data structure module1009 and its various sub-modules 1902, 1904, 1906, 1908, 1910, 1912,1914, 1916, 1918 as described above, may be disposed in a device driverfor the ACM 1011 executing on a processor 1012 of the host device 1014,such as the storage management module 1050, may be disposed in a storagecontroller 104, 1004, 1104, 1304 for the ACM 1011, and/or may compriseportions in each of a device driver and a storage controller 104, 1004,1104, 1304, or the like.

FIG. 11 depicts one embodiment of an address mapping structure 2000, alogical address space 2120, and a sequential, log-based, append-onlywriting structure 2140. The address mapping structure 2000, in oneembodiment, is maintained by the metadata module 1912, the storagecontroller 104, 1004, 1104, 1304, the storage management layer 1050, alogical-to-physical translation layer or address mapping structure, orthe like to map LBAs or other logical addresses to physical locations onthe non-volatile storage media 1110, in the ACM 1011, or the like. Forexample, in one embodiment, the metadata module 1912 may use the addressmapping structure 2000 to determine and track which portions ofpersistent data structures are stored in volatile ACM buffers 1013 andwhich portions of persistent data structures are stored in thenon-volatile memory medium 1110, with each discrete portion of apersistent data structure associated with a range of logical addresses.

While the depicted embodiment is described primarily with regard to thenon-volatile storage media 1110, in other embodiments, the addressmapping structure 2000 may map other logical identifiers of persistentdata structures to locations in the auto-commit buffers 1013 and/or thenon-volatile storage media 110, or the like. The address mappingstructure 2000, in the depicted embodiment, is a B-tree with severalentries. In the depicted embodiment, the nodes of the address mappingstructure 2000 include direct references to physical locations in thenon-volatile storage device 1102. In other embodiments, the addressmapping structure 2000 may include links that map to entries in areverse map, or the like. The address mapping structure 2000, in variousembodiments, may be used either with or without a reverse map. In otherembodiments, the references in the address mapping structure 2000 mayinclude alpha-numerical characters, hexadecimal characters, pointers,links, and the like.

The address mapping structure 2000, in the depicted embodiment, includesa plurality of nodes. Each node, in the depicted embodiment, is capableof storing two entries. In other embodiments, each node may be capableof storing a greater number of entries, the number of entries at eachlevel may change as the address mapping structure 2000 grows or shrinksthrough use, or the like.

Each entry, in the depicted embodiment, maps a variable length range ofLBAs of the non-volatile storage device 1102 to a physical location inthe storage media 1110 for the non-volatile storage device 1102.Further, while variable length ranges of LBAs, in the depictedembodiment, are represented by a starting address and an ending address,in other embodiments, a variable length range of LBAs may be representedby a starting address and a length, or the like. In one embodiment, thecapital letters ‘A’ through ‘M’ represent a logical or physical eraseblock in the physical storage media 1110 of the non-volatile storagedevice 1102 that stores the data of the corresponding range of LBAs. Inother embodiments, the capital letters may represent other physicaladdresses or locations of the non-volatile storage device 1102. In thedepicted embodiment, the capital letters ‘A’ through ‘M’ are alsodepicted in the log-based writing structure 2140 which represents thephysical storage media 1110 of the non-volatile storage device 1102.

In the depicted embodiment, membership in the address mapping structure2000 denotes membership (or storage) in the non-volatile storage device1102. In another embodiment, an entry may further include an indicatorof whether the non-volatile storage device 1102 stores datacorresponding to a logical block within the range of LBAs, data of areverse map, and/or other data.

In the depicted embodiment, the root node 2008 includes entries 2102,2104 with noncontiguous ranges of LBAs. A “hole” exists at LBA “208”between the two entries 2102, 2104 of the root node. In one embodiment,a “hole” indicates that the non-volatile storage device 1102 does notstore data corresponding to one or more LBAs corresponding to the“hole.” In one embodiment, the non-volatile storage device 1102 supportsblock I/O requests (read, write, trim, etc.) with multiple contiguousand/or noncontiguous ranges of LBAs (e.g., ranges that include one ormore “holes” in them). A “hole,” in one embodiment, may be the result ofa single block I/O request with two or more noncontiguous ranges ofLBAs. In a further embodiment, a “hole” may be the result of severaldifferent block I/O requests with LBA ranges bordering the “hole.”

In the depicted embodiment, similar “holes” or noncontiguous ranges ofLBAs exist between the entries 2106, 2108 of the node 2014, between theentries 2110, 2112 of the left child node of the node 2014, betweenentries 2114, 2116 of the node 2018, and between entries of the node2118. In one embodiment, similar “holes” may also exist between entriesin parent nodes and child nodes. For example, in the depictedembodiment, a “hole” of LBAs “060-071” exists between the left entry2106 of the node 2014 and the right entry 2112 of the left child node ofthe node 2014.

The “hole” at LBA “003,” in the depicted embodiment, can also be seen inthe logical address space 2120 of the non-volatile storage device 1102at logical address “003” 2130. The hash marks at LBA “003” 2140represent an empty location, or a location for which the non-volatilestorage device 1102 does not store data. The “hole” at LBA 2134 in thelogical address space 2120, is due to one or more block I/O requestswith noncontiguous ranges, a trim or other deallocation command to thenon-volatile storage device 1102, or the like. The address mappingstructure 2000 supports “holes,” noncontiguous ranges of LBAs, and thelike due to the sparse and/or thinly provisioned nature of the logicaladdress space 2120.

The logical address space 2120 of the non-volatile storage device 1102,in the depicted embodiment, is sparse and/or thinly provisioned, and islarger than the physical storage capacity and corresponding storagedevice address space of the non-volatile storage device 1102. In thedepicted embodiment, the non-volatile storage device 1102 has a 64 bitlogical address space 2120 beginning at logical address “0” 2122 andextending to logical address “264-1” 2126. Because the storage deviceaddress space corresponds to only a subset of the logical address space2120 of the non-volatile storage device 1102, the rest of the logicaladdress space 2120 may be allocated, mapped, and used for otherfunctions of the non-volatile storage device 1102.

The sequential, log-based, append-only writing structure 2140, in thedepicted embodiment, is a logical representation of the physical storagemedia 1110 of the non-volatile storage device 1102. In certainembodiments, the non-volatile storage device 1102 stores datasequentially, appending data to the log-based writing structure 2140 atan append point 2144. The non-volatile storage device 1102, in a furtherembodiment, uses a storage space recovery process, such as a garbagecollection module or other storage space recovery module that re-usesnon-volatile storage media 1110 storing deallocated/unused logicalblocks. Non-volatile storage media 1110 storing deallocated/unusedlogical blocks, in the depicted embodiment, is added to an availablestorage pool 2146 for the non-volatile storage device 1102. By clearinginvalid data from the non-volatile storage device 1102, as describedabove, and adding the physical storage capacity corresponding to thecleared data back to the available storage pool 2146, in one embodiment,the log-based writing structure 2140 is cyclic, ring-like, and has atheoretically infinite capacity.

In the depicted embodiment, the append point 2144 progresses around thelog-based, append-only writing structure 2140 in a circular pattern2142. In one embodiment, the circular pattern 2142 wear balances thenon-volatile storage media 122, increasing a usable life of thenon-volatile storage media 1110. In the depicted embodiment, a garbagecollection module or other storage capacity recovery process has markedseveral blocks 2148, 2150, 2152, 2154 as invalid, represented by an “X”marking on the blocks 2148, 2150, 2152, 2154. The garbage collectionmodule, in one embodiment, will recover the physical storage capacity ofthe invalid blocks 2148, 2150, 2152, 2154 and add the recovered capacityto the available storage pool 2146. In the depicted embodiment, modifiedversions of the blocks 2148, 2150, 2152, 2154 have been appended to thelog-based writing structure 2140 as new blocks 2156, 2158, 2160, 2162 ina read, modify, write operation or the like, allowing the originalblocks 2148, 2150, 2152, 2154 to be recovered.

FIG. 12 depicts one embodiment of a method 2200 for persistent datastructures. The method 2200 begins, and the allocation module 1904associates 2202 a logical identifier with a data structure. The writemodule 1906 writes 2204 data of the data structure to a first region ofa volatile memory module 1013, which is configured to ensure that thedata is preserved in response to a trigger, as described above. Thedestage module 1908 copies 2206 the data of the data structure from thevolatile memory module 1013 to a non-volatile storage medium 110, 1110,1502 so that the data of the data structure remains associated 2202 withthe logical identifier and the method 2200 ends.

FIG. 13 depicts another embodiment of a method 2300 for persistent datastructures. The method 2300 begins, and the request module 1902determines 2302 whether a persistent data structure request has beenreceived. If no persistent data structure request has been received, therequest module 1902 continues to monitor 2302 requests. If the requestmodule 1902 has received 2304 an open request, the allocation module1904 initializes and/or opens a persistent data structure, associatingthe initialized 2308 persistent data structure with a logical identifieror the like. If the request module 1902 has received 2306 a writerequest, the write module 1906 writes data of the received write request2306 to an allocated region of the ACM buffers 1013, where the destagemodule 1908 may copy the data to the non-volatile memory medium 110,1110, 1502. If the request module 1902 received 2302 a different type ofrequest, an associated module satisfies 2312 the received 2302persistent data structure request (e.g., the destage module 1908destages data to satisfy 2312 a synchronization or destage request, theread module 1914 provides data of a persistent data structure to satisfy2312 a read request, the close module 1916 closes a persistent datastructure to satisfy a close request, the map module 1918 maps a regionof the ACM 1013, a persistent data structure, or the like into virtualmemory of a client on the host device 1014 to satisfy a map request, orthe like) and the method 2300 continues.

A means for satisfying one or more requests for a persistent datastructure comprising data stored in a volatile buffer 1013 and datastored in a non-volatile recording medium 110, 1110, 1502, in variousembodiments, may include a persistent data structure module 1009, arequest module 1902, an allocation module 1904, a write module 1906, adestage module 1908, a read module 1914, a close module 1916, a mapmodule 1918, a file system module 1558, a storage management module1050, an auto-commit memory module 1011, a block device interface 1520,a memory semantic interface 1522, a SML API 1019, a device driver, astorage controller 104, 1004, 1104, 1304, a processor 1012, other logichardware, and/or other executable code stored on a computer readablestorage medium. Other embodiments may include similar or equivalentmeans for satisfying one or more requests for a persistent datastructure.

A means for committing data stored in a volatile buffer 1013 to anon-volatile recording medium 110, 1110, 1502, in various embodiments,may include a destage module 1908, an auto-commit memory module 1011, anauto-commit buffer 1013, a commit management apparatus 1122, a commitagent 1020, a write data pipeline 106, a storage controller 104, 1004,1104, 1304, a processor 1012, other logic hardware, and/or otherexecutable code stored on a computer readable storage medium. Otherembodiments may include similar or equivalent means for committing data.

A means for providing access to a persistent data structure from anon-volatile recording medium 110, 1110, 1502 after a restart eventusing a logical identifier associated with the persistent datastructure, in various embodiments, may include a persistent datastructure module 1009, a request module 1902, a read module 1914, a mapmodule 1918, a file system module 1558, a storage management module1050, an auto-commit memory module 1011, a block device interface 1520,a memory semantic interface 1522, a SML API 1019, a device driver, astorage controller 104, 1004, 1104, 1304, a processor 1012, other logichardware, and/or other executable code stored on a computer readablestorage medium. Other embodiments may include similar or equivalentmeans for providing access to a persistent data structure.

A means for enforcing an append-only rule for a persistent datastructure so that data of the data structure is not overwritten, invarious embodiments, may include a persistent data structure module1009, an enforcement module 1910, a request module 1902, a file systemmodule 1558, a storage management module 1050, an auto-commit memorymodule 1011, a block device interface 1520, a memory semantic interface1522, a SML API 1019, a device driver, a storage controller 104, 1004,1104, 1304, a processor 1012, other logic hardware, and/or otherexecutable code stored on a computer readable storage medium. Otherembodiments may include similar or equivalent means for enforcing anappend-only rule.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the disclosure is, therefore,indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A method comprising: writing data of a persistentdata structure from a host to an auto-commit memory, wherein: the hostis a computing device comprising a bus, the auto-commit memory is ahardware device with a single connection to the bus, the persistent datastructure is associated with a logical identifier, the auto-commitmemory comprises a controller, a non-volatile storage medium, and aplurality of auto-commit memory buffers that receive the data, and theauto-commit memory buffers are uniformly sized regions of a volatilememory module; arming the auto-commit memory buffers that received thedata of the persistent data structure by storing metadata in theauto-commit memory buffers such that the metadata specifies addresses ofthe non-volatile storage medium for storing the data of the persistentdata structure, and such that individual auto-commit memory buffersstore their own per-buffer portions of the metadata specifying where tostore their own per-buffer portions of the data; destaging a portion ofthe data of the persistent data structure from the auto-commit memorybuffers that received the data to addresses specified by the metadatasuch that the data of the persistent data structure remains associatedwith the logical identifier; and in response to a trigger, using thecontroller to store remaining data of the persistent data structure fromthe auto-commit memory buffers to the addresses specified by themetadata, wherein storing the data is internal to the hardware devicewithout communicating via the single connection.
 2. The method of claim1, further comprising alternating between writing data of the persistentdata structure to a first auto-commit memory buffer and a secondauto-commit memory buffer while destaging data of the persistent datastructure to the non-volatile storage medium from the other of the firstauto-commit memory buffer and the second auto-commit memory buffer. 3.The method of claim 1, further comprising enforcing one or more rulesfor the persistent data structure.
 4. The method of claim 3, wherein:the persistent data structure comprises a log data structure; the one ormore rules define the log data structure as sequential and append-only;and enforcing the one or more rules comprises preventing writes to thelog data structure other than append operations.
 5. The method of claim1, further comprising tracking which data of the persistent datastructure resides in the auto-commit memory buffers and which data ofthe persistent data structure resides in the non-volatile storagemedium.
 6. The method of claim 5, further comprising providing access tothe data of the persistent data structure residing in the auto-commitmemory buffers and the data of the persistent data structure stored inthe non-volatile storage medium using the logical identifier.
 7. Themethod of claim 1, further comprising limiting a rate at which data ofthe persistent data structure is written to the auto-commit memorybuffers such that the rate is at or below a rate at which data of thepersistent data structure is destaged to the non-volatile storagemedium.
 8. The method of claim 1, further comprising increasing atransfer rate in response to an increase in an input rate, wherein: theinput rate comprises a rate at which data of the persistent datastructure is written to the auto-commit memory buffers; and the transferrate comprises a rate at which data of the persistent data structure isdestaged to the non-volatile storage medium.
 9. The method of claim 8,wherein the transfer rate is increased by increasing a quantity of datadestaged to the non-volatile storage medium per transfer operation inresponse to the input rate being below a threshold, the transfer rateincreased by increasing a number of parallel processes destaging data inresponse to the input rate being above the threshold.
 10. The method ofclaim 1, wherein destaging data of the persistent data structure fromthe auto-commit memory buffers to the non-volatile storage medium is inresponse to one or more of: an amount of data of the persistent datastructure written to the auto-commit memory buffers satisfying athreshold; an elapsed time period; a notification provided by amonitoring device associated with the auto-commit memory buffers; and arequest from a client.
 11. The method of claim 1, wherein the persistentdata structure comprises at least one of a log, a queue, a stack, atree, a linked-list, a hash, an array, a heap, and a graph datastructure.
 12. The method of claim 1, further comprising one or more of:opening the persistent data structure in response to an open requestfrom a client; writing the data of the persistent data structure to theone or more auto-commit memory buffers in response to a write requestfrom a client; destaging data of the persistent data structure from theauto-commit memory buffers to the non-volatile storage medium inresponse to a synchronize request from a client; closing the persistentdata structure in response to a close request from a client; and mappingthe auto-commit memory buffers into virtual memory of a client inresponse to a map request from a client.
 13. The method of claim 1,wherein: the logical identifier comprises a filename of a file system;and the persistent data structure is accessible as a file of the filesystem.
 14. The method of claim 1, wherein: the volatile memory modulecomprises a byte addressable write-in-place memory device; and thenon-volatile storage medium comprises a block addressable storagedevice.
 15. The method of claim 1, wherein an isolation zone of theauto-commit memory comprises the controller, the non-volatile storagemedium, the one or more auto-commit memory buffers, and a secondarypower source configured to power the controller and the auto-commitmemory buffers despite failure of the host.
 16. An apparatus comprising:a write module configured to append data to a persistent transaction logby writing the data from a host to an auto-commit memory, wherein: thehost is a computing device comprising a bus, the auto-commit memory is ahardware device with a single connection to the bus, the auto-commitmemory comprises a controller, a non-volatile memory medium, and aplurality of auto-commit memory buffers that receive the data, and theauto-commit memory buffers are uniformly sized regions of a volatilememory module; a storage management module configured to arm theauto-commit memory buffers that received the data of the persistenttransaction log by storing metadata in the auto-commit memory bufferssuch that the metadata specifies addresses of the non-volatile memorymedium for storing the data of the persistent transaction log, and suchthat individual auto-commit memory buffers store their own per-bufferportions of the metadata specifying where to store their own per-bufferportions of the data; an enforcement module configured to enforce one ormore rules preventing the data from being overwritten in the persistenttransaction log; and a commit module configured to use the controller,in response to a trigger, to store data of the persistent transactionlog from the auto-commit memory buffers to the one or more addressesspecified by the metadata, wherein storing the data is internal to thehardware device without communicating via the single connection, whereinthe write module, the storage management module, the enforcement module,and the commit module comprise one or more of logic hardware andexecutable code, the executable code stored on a non-transitory computerreadable medium.
 17. The apparatus of claim 16, further comprising adestage module configured to write the appended data from a firstauto-commit memory buffer to the non-volatile memory medium at a ratesuch that the appended data does not overrun the first auto-commitmemory buffer, the destage module comprising one or more of logichardware and executable code, the executable code stored on anon-transitory computer readable medium.
 18. The apparatus of claim 17,wherein: the write module is configured to alternate between two or moreauto-commit memory buffers for storing appended data; and the destagemodule is configured to write appended data to the non-volatile memorymedium from an auto-commit memory buffer to which data is not currentlybeing written.
 19. An apparatus comprising: means for satisfying one ormore client requests for a persistent data structure, wherein:satisfying the one or more client requests comprises writing data of apersistent data structure from a host to an auto-commit memory, the hostis a computing device comprising a bus, the auto-commit memory is ahardware device with a single connection to the bus; the auto-commitmemory comprises a controller, a non-volatile memory medium, and aplurality of auto-commit memory buffers that receive the data; theauto-commit memory buffers are uniformly sized regions of a volatilememory module; the auto-commit memory buffers are individually armed bystoring metadata in the auto-commit memory buffers such that themetadata specifies addresses of the non-volatile memory medium forstoring data of the persistent data structure, and such that individualauto-commit memory buffers store their own per-buffer portions of themetadata specifying where to store their own per-buffer portions of thedata; and the persistent data structure comprises data stored in theauto-commit memory buffers and data stored in the non-volatile memorymedium; means for using the controller, in response to a trigger, tocommit the data of the persistent data structure stored in theauto-commit memory buffers to the addresses specified by the metadata,wherein committing the data is internal to the hardware device withoutcommunicating via the single connection; and means for providing accessto the persistent data structure from the non-volatile memory mediumafter a restart event using a logical identifier associated with thepersistent data structure.
 20. The apparatus of claim 19, furthercomprising means for enforcing an append-only rule for the persistentdata structure such that data of the persistent data structure is notoverwritten.